+++ /dev/null
-From 3d99b5c3f24714d29215a6107be0a0b3d7063a20 Mon Sep 17 00:00:00 2001
-From: Sasha Levin <sashal@kernel.org>
-Date: Thu, 5 Aug 2021 10:04:43 -0700
-Subject: pipe: avoid unnecessary EPOLLET wakeups under normal loads
-
-From: Linus Torvalds <torvalds@linux-foundation.org>
-
-[ Upstream commit 3b844826b6c6affa80755254da322b017358a2f4 ]
-
-I had forgotten just how sensitive hackbench is to extra pipe wakeups,
-and commit 3a34b13a88ca ("pipe: make pipe writes always wake up
-readers") ended up causing a quite noticeable regression on larger
-machines.
-
-Now, hackbench isn't necessarily a hugely meaningful benchmark, and it's
-not clear that this matters in real life all that much, but as Mel
-points out, it's used often enough when comparing kernels and so the
-performance regression shows up like a sore thumb.
-
-It's easy enough to fix at least for the common cases where pipes are
-used purely for data transfer, and you never have any exciting poll
-usage at all. So set a special 'poll_usage' flag when there is polling
-activity, and make the ugly "EPOLLET has crazy legacy expectations"
-semantics explicit to only that case.
-
-I would love to limit it to just the broken EPOLLET case, but the pipe
-code can't see the difference between epoll and regular select/poll, so
-any non-read/write waiting will trigger the extra wakeup behavior. That
-is sufficient for at least the hackbench case.
-
-Apart from making the odd extra wakeup cases more explicitly about
-EPOLLET, this also makes the extra wakeup be at the _end_ of the pipe
-write, not at the first write chunk. That is actually much saner
-semantics (as much as you can call any of the legacy edge-triggered
-expectations for EPOLLET "sane") since it means that you know the wakeup
-will happen once the write is done, rather than possibly in the middle
-of one.
-
-[ For stable people: I'm putting a "Fixes" tag on this, but I leave it
- up to you to decide whether you actually want to backport it or not.
- It likely has no impact outside of synthetic benchmarks - Linus ]
-
-Link: https://lore.kernel.org/lkml/20210802024945.GA8372@xsang-OptiPlex-9020/
-Fixes: 3a34b13a88ca ("pipe: make pipe writes always wake up readers")
-Reported-by: kernel test robot <oliver.sang@intel.com>
-Tested-by: Sandeep Patil <sspatil@android.com>
-Tested-by: Mel Gorman <mgorman@techsingularity.net>
-Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-Signed-off-by: Sasha Levin <sashal@kernel.org>
----
- fs/pipe.c | 15 +++++++++------
- include/linux/pipe_fs_i.h | 2 ++
- 2 files changed, 11 insertions(+), 6 deletions(-)
-
-diff --git a/fs/pipe.c b/fs/pipe.c
-index 28b2e973f10e..48abe65333c4 100644
---- a/fs/pipe.c
-+++ b/fs/pipe.c
-@@ -444,9 +444,6 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
- #endif
-
- /*
-- * Epoll nonsensically wants a wakeup whether the pipe
-- * was already empty or not.
-- *
- * If it wasn't empty we try to merge new data into
- * the last buffer.
- *
-@@ -455,9 +452,9 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
- * spanning multiple pages.
- */
- head = pipe->head;
-- was_empty = true;
-+ was_empty = pipe_empty(head, pipe->tail);
- chars = total_len & (PAGE_SIZE-1);
-- if (chars && !pipe_empty(head, pipe->tail)) {
-+ if (chars && !was_empty) {
- unsigned int mask = pipe->ring_size - 1;
- struct pipe_buffer *buf = &pipe->bufs[(head - 1) & mask];
- int offset = buf->offset + buf->len;
-@@ -590,8 +587,11 @@ out:
- * This is particularly important for small writes, because of
- * how (for example) the GNU make jobserver uses small writes to
- * wake up pending jobs
-+ *
-+ * Epoll nonsensically wants a wakeup whether the pipe
-+ * was already empty or not.
- */
-- if (was_empty) {
-+ if (was_empty || pipe->poll_usage) {
- wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
- kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
- }
-@@ -654,6 +654,9 @@ pipe_poll(struct file *filp, poll_table *wait)
- struct pipe_inode_info *pipe = filp->private_data;
- unsigned int head, tail;
-
-+ /* Epoll has some historical nasty semantics, this enables them */
-+ pipe->poll_usage = 1;
-+
- /*
- * Reading pipe state only -- no need for acquiring the semaphore.
- *
-diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
-index 5d2705f1d01c..fc5642431b92 100644
---- a/include/linux/pipe_fs_i.h
-+++ b/include/linux/pipe_fs_i.h
-@@ -48,6 +48,7 @@ struct pipe_buffer {
- * @files: number of struct file referring this pipe (protected by ->i_lock)
- * @r_counter: reader counter
- * @w_counter: writer counter
-+ * @poll_usage: is this pipe used for epoll, which has crazy wakeups?
- * @fasync_readers: reader side fasync
- * @fasync_writers: writer side fasync
- * @bufs: the circular array of pipe buffers
-@@ -70,6 +71,7 @@ struct pipe_inode_info {
- unsigned int files;
- unsigned int r_counter;
- unsigned int w_counter;
-+ unsigned int poll_usage;
- struct page *tmp_page;
- struct fasync_struct *fasync_readers;
- struct fasync_struct *fasync_writers;
---
-2.30.2
-
ovs-clear-skb-tstamp-in-forwarding-path.patch
iommu-vt-d-consolidate-duplicate-cache-invaliation-c.patch
iommu-vt-d-fix-incomplete-cache-flush-in-intel_pasid.patch
-pipe-avoid-unnecessary-epollet-wakeups-under-normal-.patch
r8152-fix-writing-usb_bp2_en.patch
i40e-fix-atr-queue-selection.patch
iavf-fix-ping-is-lost-after-untrusted-vf-had-tried-t.patch
+++ /dev/null
-From e1a59cd6661205fa704484f06408751eb5451a5d Mon Sep 17 00:00:00 2001
-From: Sasha Levin <sashal@kernel.org>
-Date: Thu, 5 Aug 2021 10:04:43 -0700
-Subject: pipe: avoid unnecessary EPOLLET wakeups under normal loads
-
-From: Linus Torvalds <torvalds@linux-foundation.org>
-
-[ Upstream commit 3b844826b6c6affa80755254da322b017358a2f4 ]
-
-I had forgotten just how sensitive hackbench is to extra pipe wakeups,
-and commit 3a34b13a88ca ("pipe: make pipe writes always wake up
-readers") ended up causing a quite noticeable regression on larger
-machines.
-
-Now, hackbench isn't necessarily a hugely meaningful benchmark, and it's
-not clear that this matters in real life all that much, but as Mel
-points out, it's used often enough when comparing kernels and so the
-performance regression shows up like a sore thumb.
-
-It's easy enough to fix at least for the common cases where pipes are
-used purely for data transfer, and you never have any exciting poll
-usage at all. So set a special 'poll_usage' flag when there is polling
-activity, and make the ugly "EPOLLET has crazy legacy expectations"
-semantics explicit to only that case.
-
-I would love to limit it to just the broken EPOLLET case, but the pipe
-code can't see the difference between epoll and regular select/poll, so
-any non-read/write waiting will trigger the extra wakeup behavior. That
-is sufficient for at least the hackbench case.
-
-Apart from making the odd extra wakeup cases more explicitly about
-EPOLLET, this also makes the extra wakeup be at the _end_ of the pipe
-write, not at the first write chunk. That is actually much saner
-semantics (as much as you can call any of the legacy edge-triggered
-expectations for EPOLLET "sane") since it means that you know the wakeup
-will happen once the write is done, rather than possibly in the middle
-of one.
-
-[ For stable people: I'm putting a "Fixes" tag on this, but I leave it
- up to you to decide whether you actually want to backport it or not.
- It likely has no impact outside of synthetic benchmarks - Linus ]
-
-Link: https://lore.kernel.org/lkml/20210802024945.GA8372@xsang-OptiPlex-9020/
-Fixes: 3a34b13a88ca ("pipe: make pipe writes always wake up readers")
-Reported-by: kernel test robot <oliver.sang@intel.com>
-Tested-by: Sandeep Patil <sspatil@android.com>
-Tested-by: Mel Gorman <mgorman@techsingularity.net>
-Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-Signed-off-by: Sasha Levin <sashal@kernel.org>
----
- fs/pipe.c | 15 +++++++++------
- include/linux/pipe_fs_i.h | 2 ++
- 2 files changed, 11 insertions(+), 6 deletions(-)
-
-diff --git a/fs/pipe.c b/fs/pipe.c
-index 8e6ef62aeb1c..678dee2a8228 100644
---- a/fs/pipe.c
-+++ b/fs/pipe.c
-@@ -444,9 +444,6 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
- #endif
-
- /*
-- * Epoll nonsensically wants a wakeup whether the pipe
-- * was already empty or not.
-- *
- * If it wasn't empty we try to merge new data into
- * the last buffer.
- *
-@@ -455,9 +452,9 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
- * spanning multiple pages.
- */
- head = pipe->head;
-- was_empty = true;
-+ was_empty = pipe_empty(head, pipe->tail);
- chars = total_len & (PAGE_SIZE-1);
-- if (chars && !pipe_empty(head, pipe->tail)) {
-+ if (chars && !was_empty) {
- unsigned int mask = pipe->ring_size - 1;
- struct pipe_buffer *buf = &pipe->bufs[(head - 1) & mask];
- int offset = buf->offset + buf->len;
-@@ -590,8 +587,11 @@ out:
- * This is particularly important for small writes, because of
- * how (for example) the GNU make jobserver uses small writes to
- * wake up pending jobs
-+ *
-+ * Epoll nonsensically wants a wakeup whether the pipe
-+ * was already empty or not.
- */
-- if (was_empty) {
-+ if (was_empty || pipe->poll_usage) {
- wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
- kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
- }
-@@ -654,6 +654,9 @@ pipe_poll(struct file *filp, poll_table *wait)
- struct pipe_inode_info *pipe = filp->private_data;
- unsigned int head, tail;
-
-+ /* Epoll has some historical nasty semantics, this enables them */
-+ pipe->poll_usage = 1;
-+
- /*
- * Reading pipe state only -- no need for acquiring the semaphore.
- *
-diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
-index 5d2705f1d01c..fc5642431b92 100644
---- a/include/linux/pipe_fs_i.h
-+++ b/include/linux/pipe_fs_i.h
-@@ -48,6 +48,7 @@ struct pipe_buffer {
- * @files: number of struct file referring this pipe (protected by ->i_lock)
- * @r_counter: reader counter
- * @w_counter: writer counter
-+ * @poll_usage: is this pipe used for epoll, which has crazy wakeups?
- * @fasync_readers: reader side fasync
- * @fasync_writers: writer side fasync
- * @bufs: the circular array of pipe buffers
-@@ -70,6 +71,7 @@ struct pipe_inode_info {
- unsigned int files;
- unsigned int r_counter;
- unsigned int w_counter;
-+ unsigned int poll_usage;
- struct page *tmp_page;
- struct fasync_struct *fasync_readers;
- struct fasync_struct *fasync_writers;
---
-2.30.2
-
iommu-vt-d-fix-incomplete-cache-flush-in-intel_pasid.patch
drm-i915-skip-display-interruption-setup-when-displa.patch
drm-i915-tweaked-wa_14010685332-for-all-pchs.patch
-pipe-avoid-unnecessary-epollet-wakeups-under-normal-.patch
drm-amd-display-use-dcn30-watermark-calc-for-dcn301.patch
net-mscc-ocelot-allow-forwarding-from-bridge-ports-t.patch
mptcp-fix-memory-leak-on-address-flush.patch
projects / thirdparty / kernel / stable-queue.git / commitdiff
