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(cst-prg-92-135.cust.vodafone.cz. [46.135.92.135]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45d9ec3ac86sm18819419f8f.14.2026.05.15.19.18.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 15 May 2026 19:18:58 -0700 (PDT) From: Mateusz Guzik To: brauner@kernel.org Cc: viro@zeniv.linux.org.uk, jack@suse.cz, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Mateusz Guzik Subject: [MEH PATCH] fs/pipe: write to ->poll_usage only once Date: Sat, 16 May 2026 04:18:52 +0200 Message-ID: <20260516021852.256932-1-mjguzik@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 --- disclaimer: could not be bothered to bench this fs/pipe.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/pipe.c b/fs/pipe.c index 9841648c9cf3..e37c79935ecb 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -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. -- 2.48.1