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bf368e4e70
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Eric Dumazet bf368e4e70 net: Avoid extra wakeups of threads blocked in wait_for_packet() 
In 2.6.25 we added UDP mem accounting.

This unfortunatly added a penalty when a frame is transmitted, since
we have at TX completion time to call sock_wfree() to perform necessary
memory accounting. This calls sock_def_write_space() and utimately
scheduler if any thread is waiting on the socket.
Thread(s) waiting for an incoming frame was scheduled, then had to sleep
again as event was meaningless.

(All threads waiting on a socket are using same sk_sleep anchor)

This adds lot of extra wakeups and increases latencies, as noted
by Christoph Lameter, and slows down softirq handler.

Reference : http://marc.info/?l=linux-netdev&m=124060437012283&w=2 

Fortunatly, Davide Libenzi recently added concept of keyed wakeups
into kernel, and particularly for sockets (see commit
37e5540b3c 
epoll keyed wakeups: make sockets use keyed wakeups)

Davide goal was to optimize epoll, but this new wakeup infrastructure
can help non epoll users as well, if they care to setup an appropriate
handler.

This patch introduces new DEFINE_WAIT_FUNC() helper and uses it
in wait_for_packet(), so that only relevant event can wakeup a thread
blocked in this function.

Trace of function calls from bnx2 TX completion bnx2_poll_work() is :
__kfree_skb()
 skb_release_head_state()
  sock_wfree()
   sock_def_write_space()
    __wake_up_sync_key()
     __wake_up_common()
      receiver_wake_function() : Stops here since thread is waiting for an INPUT


Reported-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2009-04-28 02:24:21 -07:00
..
acpi Merge branches 'release', 'APERF', 'ARAT', 'misc', 'kelvin', 'device-lock' and 'bjorn.notify' into release 2009-04-07 18:18:42 -04:00
asm-arm S3C24XX: Move and update IIS headers 2009-03-05 12:00:59 +00:00
asm-generic percpu: unbreak alpha percpu 2009-04-10 21:36:18 +02:00
asm-h8300
asm-m32r Merge branch 'tracing-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2009-04-05 11:04:19 -07:00
crypto crypto: zlib - New zlib crypto module, using pcomp 2009-03-04 15:16:19 +08:00
drm drm: remove unused "can_grow" parameter from drm_crtc_helper_initial_config 2009-04-03 10:21:44 +10:00
keys
linux net: Avoid extra wakeups of threads blocked in wait_for_packet() 2009-04-28 02:24:21 -07:00
math-emu
media V4L/DVB (11381): ivtv/cx18: remove VIDIOC_INT_S_AUDIO_ROUTING debug support. 2009-04-06 21:44:28 -03:00
mtd make MTD headers use strict integer types 2009-03-26 18:14:17 +01:00
net Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/kaber/nf-2.6 2009-04-16 16:32:29 -07:00
pcmcia
rdma Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next-2.6 2009-03-26 15:54:36 -07:00
rxrpc
scsi PM/Hibernate: Wait for SCSI devices scan to complete during resume 2009-04-13 11:37:07 -07:00
sound V4L/DVB (10771): tea575x-tuner: convert it to V4L2 API 2009-03-30 12:43:02 -03:00
trace tracing/syscalls: use a dedicated file header 2009-04-09 05:43:32 +02:00
video tdfxfb: move I2C functionality into the tdfxfb 2009-04-07 08:31:08 -07:00
xen
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