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fs/pipe: write to ->poll_usage only once

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Both GNU and BSD makes share a "token pipe" between their instances, as
a result a -j $BIGNUM invocation results in multicore perf problems in
the poll handler.

Avoiding the store will reduce it a little bit. However, the crux of the
problem is the locked queuing up in poll_wait().

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://patch.msgid.link/20260516021852.256932-1-mjguzik@gmail.com
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
Mateusz Guzik
2026-05-16 04:18:52 +02:00
committed by Christian Brauner
parent 50d377ef12
commit 7dc6acb3d5
1 changed files with 2 additions and 1 deletions
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3
fs/pipe.c
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@@ -664,7 +664,8 @@ pipe_poll(struct file *filp, poll_table *wait)
union pipe_index idx;
/* Epoll has some historical nasty semantics, this enables them */
WRITE_ONCE(pipe->poll_usage, true);
if (unlikely(!READ_ONCE(pipe->poll_usage)))
WRITE_ONCE(pipe->poll_usage, true);
/*
* Reading pipe state only -- no need for acquiring the semaphore.