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Date: Wed, 11 May 2022 09:20:51 +0200 From: Arnd Bergmann <arnd@...db.de> To: Waiman Long <longman@...hat.com> Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>, Boqun Feng <boqun.feng@...il.com>, Arnd Bergmann <arnd@...db.de>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 2/2] locking/qrwlock: Reduce cacheline contention for rwlocks used in interrupt context On Tue, May 10, 2022 at 9:21 PM Waiman Long <longman@...hat.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@...hat.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@...db.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/
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