Messages in this thread | | | From | Arnd Bergmann <> | Date | Wed, 11 May 2022 09:20:51 +0200 | Subject | Re: [PATCH 2/2] locking/qrwlock: Reduce cacheline contention for rwlocks used in interrupt context |
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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/
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