From: Jens Axboe <axboe@kernel.dk>
To: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>, Peter Zijlstra <peterz@infradead.org>
Subject: [PATCH] task_work: only grab task signal lock when needed
Date: Tue, 11 Aug 2020 08:25:20 -0600 [thread overview]
Message-ID: <0028d3ea-4d05-405f-b457-75c83d381d89@kernel.dk> (raw)
If JOBCTL_TASK_WORK is already set on the targeted task, then we need
not go through {lock,unlock}_task_sighand() to set it again and queue
a signal wakeup. This is safe as we're checking it _after adding the
new task_work with cmpxchg().
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
Tested this with an intensive task_work based io_uring workload, and
the benefits are quite large.
diff --git a/kernel/task_work.c b/kernel/task_work.c
index 5c0848ca1287..cbf8cab6e864 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -42,7 +42,8 @@ task_work_add(struct task_struct *task, struct callback_head *work, int notify)
set_notify_resume(task);
break;
case TWA_SIGNAL:
- if (lock_task_sighand(task, &flags)) {
+ if (!(READ_ONCE(task->jobctl) & JOBCTL_TASK_WORK) &&
+ lock_task_sighand(task, &flags)) {
task->jobctl |= JOBCTL_TASK_WORK;
signal_wake_up(task, 0);
unlock_task_sighand(task, &flags);
--
Jens Axboe
next reply other threads:[~2020-08-11 14:25 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-11 14:25 Jens Axboe [this message]
2020-08-11 15:23 ` [PATCH] task_work: only grab task signal lock when needed Oleg Nesterov
2020-08-11 16:45 ` Jens Axboe
2020-08-12 14:54 ` Oleg Nesterov
2020-08-12 20:06 ` Peter Zijlstra
2020-08-12 23:13 ` Jens Axboe
2020-08-13 11:48 ` Oleg Nesterov
2020-08-13 15:07 Jens Axboe
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=0028d3ea-4d05-405f-b457-75c83d381d89@kernel.dk \
--to=axboe@kernel.dk \
--cc=linux-kernel@vger.kernel.org \
--cc=oleg@redhat.com \
--cc=peterz@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).