Commit graph

27246 commits

Author SHA1 Message Date
Jack Morgenstein
9874e74655 IB/mad: Check GID/LID when matching requests
Check GID/LID for requester side when searching for request which
matches received response.  This is in order to guarantee uniqueness
if the same TID is used when requesting via multiple source LIDs (when
LMC is not zero).  Use ports' cached LMC to perform the check.

Further, do not perform LID check for direct-routed packets, since
the permissive LID makes a proper check impossible.

Signed-off-by: Jack Morgenstein <jackm@mellanox.co.il>
Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:34 -07:00
Jack Morgenstein
6fb9cdbf2c IB: Add caching of ports' LMC
Add an LMC cache to struct ib_device, and add a function
ib_get_cached_lmc() to query the cache.

Signed-off-by: Jack Morgenstein <jackm@mellanox.co.il>
Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:34 -07:00
Michael S. Tsirkin
856c256f88 IB/cm: remove unneeded flush_workqueue
destroy_workqueue() already does flush_workqueue().

Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Sean Hefty <sean.hefty@intel.com>
2006-06-17 20:37:33 -07:00
Sean Hefty
4be10c1e6d IB/ucm: convert semaphore to mutex
Convert semaphore in ib_ucm_file to a real mutex.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:33 -07:00
Roland Dreier
6bfa24fa3e IB/srp: Get rid of "Target has req_lim 0" messages
It's perfectly valid for a connection to an SRP target to have a
request limit of 0, so get rid of the message about it, which can spam
kernel logs even with printk_ratelimit().  Keep a count of such events
in a "zero_req_lim" SCSI host attribute instead, so someone who cares
can look at the statistics.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:33 -07:00
Ishai Rabinovitz
b7ac4ab497 IB/srp: Handle DREQ events from CM
Handle IB_CM_DREQ_ERROR and IB_CM_DREQ_RECEIVED events from the CM,
instead of just printing "Unhandled CM event".  In the case of
DREQ_ERROR, just ignore the event -- a TIMEWAIT_EXIT will be generated
also.  For DREQ_RECEIVED, send a DREP in response to shut the
connection down cleanly.

Signed-off-by: Ishai Rabinovitz <ishai@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:32 -07:00
Roland Dreier
ac83cbaa9a IPoIB: Mention RFC numbers in documentation
Now that the IETF has released RFCs covering IPoIB, give the numbers in
the documentation for IPoIB.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:32 -07:00
Vu Pham
74b0a15b5e IB/srp: Allow sg_tablesize to be adjusted
Make the sg_tablesize used by SRP adjustable at module load time via a
module parameter.  Calculate the corresponding IU length required to
support this.

Signed-off-by: Vu Pham <vu@mellanox.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:32 -07:00
Vu Pham
52fb2b50c4 IB/srp: Allow cmd_per_lun to be set per target port
Allow userspace to throttle traffic on a given connection to a target
port by adding "max_cmd_per_lun=xyz" to lower the cmd_per_lun value
set for that scsi_host.

Signed-off-by: Vu Pham <vu@mellanox.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:31 -07:00
Ishai Rabinovitz
0c5b395239 IB/srp: Clean up loop in srp_remove_one()
Interrupts will always be enabled in srp_remove_one(), so
spin_lock_irq() can be used instead of spin_lock_irqsave().
Also, the loop takes target->scsi_host->host_lock, so target->state
can just be set to SRP_TARGET_REMOVED witout testing the old value.

Signed-off-by: Ishai Rabinovitz <ishai@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:31 -07:00
Roland Dreier
403a496fd4 IB: Make needlessly global ib_mad_cache static
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:31 -07:00
Matthew Wilcox
b3589fd490 IB/srp: Change target_mutex to a spinlock
The SRP driver never sleeps while holding target_mutex, and it's just
used to protect some simple list operations, so hold times will be
short.  So just convert it to a spinlock, which is smaller and faster.

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:30 -07:00
Matthew Wilcox
549c5fc2c8 IB/srp: Get rid of unneeded use of list_for_each_entry_safe()
list_for_each_entry_safe() is used in one place where the list isn't
modified.  So just change it to list_for_each_entry().

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:30 -07:00
Matthew Wilcox
1962a4a1e4 IB/srp: Use SCAN_WILD_CARD from SCSI headers
SCAN_WILD_CARD is indeed available from <scsi/scsi.h>, which is
already included.  So get rid of private hack.

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:30 -07:00
Roland Dreier
e9cd59418f IB/mthca: Convert FW commands to use wait_for_completion_timeout()
The kernel has had wait_for_completion_timeout() for a long time now.
mthca should use it to handle FW commands timing out, instead of
implementing the same thing in a much more complicated way by using
wait_for_completion() along with a timer that does complete().

Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:30 -07:00
Roland Dreier
f5358a172f IB/srp: Use FMRs to map gather/scatter lists
Create an SRP FMR pool on HCAs that support FMRs, and use FMRs to map
gather/scatter lists that have more than one entry into a single
memory region that appears virtually contiguous to the SRP target
(which is the RDMA initiator).

This patch bails out on FMR mapping for SCSI commands where the
gather/scatter list cannot be mapped into a single FMR because there
are sub-page-sized entries in middle of the list.  An unaligned
start or end of the list is OK.

Based on a patch by Vu Pham <vuhuong@mellanox.com>.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:29 -07:00
Michael S. Tsirkin
a26026c122 IB/mthca: Remove dead code
Kill some dead code in mthca_eq.c

Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:29 -07:00
Sean Hefty
e51060f08a IB: IP address based RDMA connection manager
Kernel connection management agent over InfiniBand that connects based
on IP addresses.  The agent defines a generic RDMA connection
abstraction to support clients wanting to connect over different RDMA
devices.

The agent also handles RDMA device hotplug events on behalf of clients.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:29 -07:00
Sean Hefty
7025fcd36b IB: address translation to map IP toIB addresses (GIDs)
Add an address translation service that maps IP addresses to
InfiniBand GID addresses using IPoIB.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:28 -07:00
Sean Hefty
a1e8733e55 [NET]: Export ip_dev_find()
Export ip_dev_find() to allow locating a net_device given an IP address.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:28 -07:00
Sean Hefty
6e61d04f2d IB/cm: Match connection requests based on private data
Extend matching connection requests to listens in the InfiniBand CM to
include private data checks.

This allows applications to listen on the same service identifier,
with private data directing the request to the appropriate application.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:28 -07:00
Sean Hefty
6a9af2e18a IB: common handling for marshalling parameters to/from userspace
Provide common handling for marshalling data between userspace clients
and kernel InfiniBand drivers.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:27 -07:00
Michael S. Tsirkin
4e56ea794e IB/mthca: memfree completion with error FW bug workaround
Memfree firmware is in rare cases reporting WQE index == base - 1 in
receive completion with error, instead of (rq size - 1); base is 0 in
mthca.  Here is a patch to avoid kernel crash and report a correct WR
id in this case.

Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:20 -07:00
Michael S. Tsirkin
13aa6ecb47 IB/mthca: restore missing PCI registers after reset
mthca does not restore the following PCI-X/PCI Express registers after reset:
  PCI-X device: PCI-X command register
  PCI-X bridge: upstream and downstream split transaction registers
  PCI Express : PCI Express device control and link control registers

This causes instability and/or bad performance on systems where one of
these registers is set to a non-default value by BIOS.

Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
2006-06-17 20:37:00 -07:00
Linus Torvalds
427abfa28a Linux v2.6.17
Being named "Crazed Snow-Weasel" instills a lot of confidence in this
release, so I'm sure this will be one of the better ones.
2006-06-17 18:49:35 -07:00
Arnd Bergmann
ce221982e0 [PATCH] powerpc: enable CPU_FTR_CI_LARGE_PAGE for cell
Reflect the fact that the Cell Broadband Engine supports 64k
pages by adding the bit to the CPU features.

Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-17 10:56:24 -07:00
Arnd Bergmann
19242b2407 [PATCH] powerpc: Fix 64k pages on non-partitioned machines
The page size encoding passed to tlbie is incorrect for new-style
large pages.  This fixes it.  This doesn't affect anything on older
machines because mmu_psize_defs[psize].penc (the page size encoding)
is 0 for 4k and 16M pages (the two are distinguished by a separate "is
a large page" bit).

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-17 10:56:24 -07:00
Oleg Nesterov
f53ae1dc34 [PATCH] arm_timer: remove a racy and obsolete PF_EXITING check
arm_timer() checks PF_EXITING to prevent BUG_ON(->exit_state)
in run_posix_cpu_timers().

However, for some reason it does so only for CPUCLOCK_PERTHREAD
case (which is imho wrong).

Also, this check is not reliable, PF_EXITING could be set on
another cpu without any locks/barriers just after the check,
so it can't prevent from attaching the timer to the exiting
task.

The previous patch makes this check unneeded.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-17 10:52:13 -07:00
Oleg Nesterov
30f1e3dd8c [PATCH] run_posix_cpu_timers: remove a bogus BUG_ON()
do_exit() clears ->it_##clock##_expires, but nothing prevents
another cpu to attach the timer to exiting process after that.
arm_timer() tries to protect against this race, but the check
is racy.

After exit_notify() does 'write_unlock_irq(&tasklist_lock)' and
before do_exit() calls 'schedule() local timer interrupt can find
tsk->exit_state != 0. If that state was EXIT_DEAD (or another cpu
does sys_wait4) interrupted task has ->signal == NULL.

At this moment exiting task has no pending cpu timers, they were
cleanuped in __exit_signal()->posix_cpu_timers_exit{,_group}(),
so we can just return from irq.

John Stultz recently confirmed this bug, see

	http://marc.theaimsgroup.com/?l=linux-kernel&m=115015841413687

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-17 10:52:13 -07:00
Oleg Nesterov
8f17fc20bf [PATCH] check_process_timers: fix possible lockup
If the local timer interrupt happens just after do_exit() sets PF_EXITING
(and before it clears ->it_xxx_expires) run_posix_cpu_timers() will call
check_process_timers() with tasklist_lock + ->siglock held and

	check_process_timers:

		t = tsk;
		do {
			....

			do {
				t = next_thread(t);
			} while (unlikely(t->flags & PF_EXITING));
		} while (t != tsk);

the outer loop will never stop.

Actually, the window is bigger.  Another process can attach the timer
after ->it_xxx_expires was cleared (see the next commit) and the 'if
(PF_EXITING)' check in arm_timer() is racy (see the one after that).

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-17 10:52:13 -07:00
Stephen Hemminger
88d113601c [PATCH] sky2: netconsole suspend/resume interaction
A couple of fixes that should prevent crashes when using netconsole and
suspend/resume. First, netconsole poll routine shouldn't run unless the
device is up; second, the NAPI poll should be disabled during suspend.

This is only an issue on sky2, because it has to have one NAPI poll
routine for both ports on dual port boards. Normal drivers use
netif_rx_schedule_prep and that checks for netif_running.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-17 10:52:12 -07:00
Jens Axboe
991721572e [PATCH] Fix missing ret assignment in __bio_map_user() error path
If get_user_pages() returns less pages than what we asked for, we jump
to out_unmap which will return ERR_PTR(ret).  But ret can contain a
positive number just smaller than local_nr_pages, so be sure to set it
to -EFAULT always.

Problem found and diagnosed by Damien Le Moal <damien@sdl.hitachi.co.jp>

Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-17 10:52:12 -07:00
Jens Axboe
16070428d3 [PATCH] fix cdrom open
Some time ago the cdrom open routine was changed so that we call the
driver's open routine before checking to see if it is read only.  However,
if we discovered that a read write open was not possible and the open
flags required a writable open, we just returned -EROFS without calling
the driver's release routine.   This seems to work for most cdrom drivers,
but breaks the Powerpc iSeries virtual cdrom rather badly.

This just inserts the release call in the error path to balance the call
to "->open()" done by "open_for_data()".

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-17 10:44:26 -07:00
Jens Axboe
553698f944 [PATCH] cfq-iosched: fix crash in do_div()
We don't clear the seek stat values in cfq_alloc_io_context(), and if
->seek_mean is unlucky enough to be set to -36 by chance, the first
invocation of cfq_update_io_seektime() will oops with a divide by zero
in do_div().

Just memset the entire cic instead of filling invididual values
independently.

Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-14 10:22:16 -07:00
Kirill Korotaev
9cedc194a7 [PATCH] Return error in case flock_lock_file failure
If flock_lock_file() failed to allocate flock with locks_alloc_lock()
then "error = 0" is returned. Need to return some non-zero.

Signed-off-by: Pavel Emelianov <xemul@openvz.org>
Signed-off-by: Kirill Korotaev <dev@openvz.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-14 08:59:44 -07:00
Stephen Hemminger
eb35cf60e4 [PATCH] sky2: stop/start hardware idle timer on suspend/resume
The resume bug was caused not by an early interrupt but because the idle
timeout was not being stopped on suspend.  Also disable hardware IRQ's
on suspend.  Will need to revisit this with hotplug?

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-13 13:16:41 -07:00
Stephen Hemminger
8ab8fca207 [PATCH] sky2: save/restore base hardware irq during suspend/resume
The hardware should be fully shut off during suspend, and the base
irq mask restored during resume.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-13 13:16:41 -07:00
Stephen Hemminger
26ec43f132 [PATCH] sky2: fix hotplug detect during poll
If the poll routine detects no hardware available, it needs to dequeue
it self from the network poll list. Linus didn't understand NAPI.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-13 13:16:41 -07:00
Stephen Hemminger
f05267e7de [PATCH] sky2: don't hard code number of ports
It is cleaner, to not loop over both ports if only one exists.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-13 13:16:41 -07:00
Stephen Hemminger
2ccc99b7b7 [PATCH] sky2: set_power_state should be void
The set power state function is cleaner if it doesn't return anything.
The only caller that could fail is in suspend() and it can check the argument
there.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-13 13:16:40 -07:00
Randy Dunlap
5e625b0844 [PATCH] alpha: generic hweight build fix
From: Randy Dunlap <rdunlap@xenotime.net>

According to include/asm-alpha/bitops.h, only ALPHA_EV67 has hardware
hweight support, so ALPHA_EV6 needs to use GENERIC_HWEIGHT.

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Ernst Herzberg <earny@net4u.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-12 15:17:53 -07:00
Sergey Vlasov
86bc843a26 [PATCH] tmpfs: Decrement i_nlink correctly in shmem_rmdir()
shmem_rmdir() must undo the increment of i_nlink done in
shmem_get_inode() for directories, otherwise at least
IN_DELETE_SELF inotify event generation is broken.

Signed-off-by: Sergey Vlasov <vsu@altlinux.ru>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-12 14:29:04 -07:00
Robin H. Johnson
cfd95a9cf5 [PATCH] tmpfs: time granularity fix for [acm]time going backwards
I noticed a strange behavior in a tmpfs file system the other day, while
building packages - occasionally, and seemingly at random, make decided to
rebuild a target. However, only on tmpfs.

A file would be created, and if checked, it had a sub-second timestamp.
However, after an utimes related call where sub-seconds should be set, they
were zeroed instead. In the case that a file was created, and utimes(...,NULL)
was used on it in the same second, the timestamp on the file moved backwards.

After some digging, I found that this was being caused by tmpfs not having a
time granularity set, thus inheriting the default 1 second granularity.

Hugh adds: yes, we missed tmpfs when the s_time_gran mods went into 2.6.11.
Unfortunately, the granularity of CURRENT_TIME, often used in filesystems,
does not match the default granularity set by alloc_super.  A few more such
discrepancies have been found, but this is the most important to fix now.

Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>
Acked-by: Andi Kleen <ak@suse.de>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-12 13:55:52 -07:00
Linus Torvalds
5f856e8bdc Merge master.kernel.org:/pub/scm/linux/kernel/git/davem/sparc-2.6
* master.kernel.org:/pub/scm/linux/kernel/git/davem/sparc-2.6:
  [SPARC64]: Do not double-export sys_close() when CONFIG_SOLARIS_EMUL_MODULE
2006-06-12 13:46:43 -07:00
Linus Torvalds
a3b5960ebd Merge master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6
* master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6:
  [IPV4]: Increment ipInHdrErrors when TTL expires.
  [TCP]: continued: reno sacked_out count fix
  [DCCP] Ackvec: fix soft lockup in ackvec handling code
2006-06-12 13:46:27 -07:00
Linus Torvalds
37b0d1dedc Merge master.kernel.org:/home/rmk/linux-2.6-arm
* master.kernel.org:/home/rmk/linux-2.6-arm:
  [ARM] Fix Integrator and Versatile interrupt initialisation
  [ARM] 3546/1: PATCH: subtle lost interrupts bug on i.MX
  [ARM] 3547/1: PXA-OHCI: Allow platforms to specify a power budget
  [ARM] Fix Neponset IRQ handling
2006-06-12 13:45:41 -07:00
Weidong
42d1d52e69 [IPV4]: Increment ipInHdrErrors when TTL expires.
Signed-off-by: Weidong <weid@nanjing-fnst.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2006-06-12 13:09:59 -07:00
Linus Torvalds
d374c1c128 [sky2] Fix sky2 network driver suspend/resume
This fixes two independent problems: it would not save the PCI state on
suspend (and thus try to resume a nonexistent state on resume), and
while shut off, if an interrupt happened on the same shared irq, the irq
handler would react very badly to the interrupt status being an invalid
all-ones state.

Acked-by: Jeff Garzik <jgarzik@pobox.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-12 12:53:27 -07:00
Linus Torvalds
0e838b72d5 Merge branch 'upstream-linus' of master.kernel.org:/pub/scm/linux/kernel/git/jgarzik/libata-dev
* 'upstream-linus' of master.kernel.org:/pub/scm/linux/kernel/git/jgarzik/libata-dev:
  [PATCH] sata_mv: grab host lock inside eng_timeout
2006-06-12 07:47:04 -07:00
Aki M Nyrhinen
79320d7e14 [TCP]: continued: reno sacked_out count fix
From: Aki M Nyrhinen <anyrhine@cs.helsinki.fi>

IMHO the current fix to the problem (in_flight underflow in reno)
is incorrect.  it treats the symptons but ignores the problem. the
problem is timing out packets other than the head packet when we
don't have sack. i try to explain (sorry if explaining the obvious).

with sack, scanning the retransmit queue for timed out packets is
fine because we know which packets in our retransmit queue have been
acked by the receiver.

without sack, we know only how many packets in our retransmit queue the
receiver has acknowledged, but no idea which packets.

think of a "typical" slow-start overshoot case, where for example
every third packet in a window get lost because a router buffer gets
full.

with sack, we check for timeouts on those every third packet (as the
rest have been sacked). the packet counting works out and if there
is no reordering, we'll retransmit exactly the packets that were 
lost.

without sack, however, we check for timeout on every packet and end up
retransmitting consecutive packets in the retransmit queue. in our
slow-start example, 2/3 of those retransmissions are unnecessary. these
unnecessary retransmissions eat the congestion window and evetually
prevent fast recovery from continuing, if enough packets were lost.

Signed-off-by: David S. Miller <davem@davemloft.net>
2006-06-11 21:18:56 -07:00