From: Arnd Bergmann <arnd@arndb.de>
To: Waiman Long <longman@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
Boqun Feng <boqun.feng@gmail.com>, Arnd Bergmann <arnd@arndb.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] locking/qrwlock: Reduce cacheline contention for rwlocks used in interrupt context
Date: Wed, 11 May 2022 09:20:51 +0200 [thread overview]
Message-ID: <CAK8P3a3APecwzfS24Cc2f7rPdZXKU0Y9FB3RZNFTnRYnVXVQzg@mail.gmail.com> (raw)
In-Reply-To: <20220510192134.434753-2-longman@redhat.com>
On Tue, May 10, 2022 at 9:21 PM Waiman Long <longman@redhat.com> wrote:
>
> Even though qrwlock is supposed to be a fair lock, it does allow readers
> from interrupt context to spin on the lock until it can acquire it making
> it not as fair. This exception was added due to the requirement to allow
> recursive read lock in interrupt context. This can also be achieved by
> just ignoring the writer waiting bit without spinning on the lock.
>
> By making this change, we make qrwlock a bit more fair and eliminating
> the problem of cacheline bouncing for rwlocks that are used heavily in
> interrupt context, like the networking stack. This should also reduce
> the chance of lock starvation for those interrupt context rwlocks.
>
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
> include/asm-generic/qrwlock.h | 6 +++---
> kernel/locking/qrwlock.c | 17 ++++++-----------
> 2 files changed, 9 insertions(+), 14 deletions(-)
I have no opinion on the change itself, but I made sure this does
not conflict with the generic ticket spinlock changes that I merged
in the asm-generic tree, since those also touch the comments in
qrwlock.h [1]
I assume you are merging both patches through the tip tree, so
Acked-by: Arnd Bergmann <arnd@arndb.de> # for asm-generic
If you want me to pick them up in the asm-generic tree instead,
just let me know.
Arnd
[1] https://lore.kernel.org/lkml/20220509222956.2886-4-palmer@rivosinc.com/
next prev parent reply other threads:[~2022-05-11 7:21 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-10 19:21 [PATCH 1/2] locking/qrwlock: Change "queue rwlock" to "queued rwlock" Waiman Long
2022-05-10 19:21 ` [PATCH 2/2] locking/qrwlock: Reduce cacheline contention for rwlocks used in interrupt context Waiman Long
2022-05-11 7:20 ` Arnd Bergmann [this message]
2022-05-11 12:01 ` Waiman Long
2022-05-11 8:30 ` Peter Zijlstra
2022-05-11 12:44 ` Waiman Long
2022-05-11 13:34 ` Peter Zijlstra
2022-05-11 16:00 ` Waiman Long
2022-05-11 19:39 ` [tip: locking/core] locking/qrwlock: Change "queue rwlock" to "queued rwlock" tip-bot2 for Waiman Long
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