From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-c6x-dev@linux-c6x.org,
uclinux-h8-devel@lists.sourceforge.jp,
linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org,
linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org,
nios2-dev@lists.rocketboards.org, openrisc@lists.librecores.org,
linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
linux-sh@vger.kernel.org, sparclinux@vger.kernel.org,
linux-um@lists.infradead.org, linux-xtensa@linux-xtensa.org,
linux-arch@vger.kernel.org, x86@kernel.org,
Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Davidlohr Bueso <dave@stgolabs.net>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Tim Chen <tim.c.chen@linux.intel.com>
Subject: Re: [PATCH v4 0/3] locking/rwsem: Rwsem rearchitecture part 0
Date: Thu, 14 Feb 2019 17:05:27 -0500 [thread overview]
Message-ID: <5c373ba6-419e-c4d5-965f-a566a6182b28@redhat.com> (raw)
In-Reply-To: <20190214103715.GI32494@hirez.programming.kicks-ass.net>
On 02/14/2019 05:37 AM, Peter Zijlstra wrote:
> On Wed, Feb 13, 2019 at 05:00:14PM -0500, Waiman Long wrote:
>> v4:
>> - Remove rwsem-spinlock.c and make all archs use rwsem-xadd.c.
>>
>> v3:
>> - Optimize __down_read_trylock() for the uncontended case as suggested
>> by Linus.
>>
>> v2:
>> - Add patch 2 to optimize __down_read_trylock() as suggested by PeterZ.
>> - Update performance test data in patch 1.
>>
>> The goal of this patchset is to remove the architecture specific files
>> for rwsem-xadd to make it easer to add enhancements in the later rwsem
>> patches. It also removes the legacy rwsem-spinlock.c file and make all
>> the architectures use one single implementation of rwsem - rwsem-xadd.c.
>>
>> Waiman Long (3):
>> locking/rwsem: Remove arch specific rwsem files
>> locking/rwsem: Remove rwsem-spinlock.c & use rwsem-xadd.c for all
>> archs
>> locking/rwsem: Optimize down_read_trylock()
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>
> with the caveat that I'm happy to exchange patch 3 back to my earlier
> suggestion in case Will expesses concerns wrt the ARM64 performance of
> Linus' suggestion.
I inserted a few lock event counters into the rwsem trylock code:
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
/*
* Optimize for the case when the rwsem is not locked at all.
*/
long tmp = RWSEM_UNLOCKED_VALUE;
lockevent_inc(rwsem_rtrylock);
do {
if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
tmp + RWSEM_ACTIVE_READ_BIAS)) {
rwsem_set_reader_owned(sem);
return 1;
}
lockevent_inc(rwsem_rtrylock_retry);
} while (tmp >= 0);
lockevent_inc(rwsem_rtrylock_fail);
return 0;
}
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
long tmp;
lockevent_inc(rwsem_wtrylock);
tmp = atomic_long_cmpxchg_acquire(&sem->count, RWSEM_UNLOCKED_VALUE,
RWSEM_ACTIVE_WRITE_BIAS);
if (tmp == RWSEM_UNLOCKED_VALUE) {
rwsem_set_owner(sem);
return true;
}
lockevent_inc(rwsem_wtrylock_fail);
return false;
}
I booted the new kernel on a 4-socket 56-core 112-thread Broadwell
system. The counter values
1) After bootup:
rwsem_rtrylock=784029
rwsem_rtrylock_fail=59
rwsem_rtrylock_retry=394
rwsem_wtrylock=18284
rwsem_wtrylock_fail=230
2) After parallel kernel build (-j112):
rwsem_rtrylock=338667559
rwsem_rtrylock_fail=18
rwsem_rtrylock_retry=51
rwsem_wtrylock=17016332
rwsem_wtrylock_fail=98058
At least for these two use cases, try-for-ownership as suggested by
Linus is the right choice.
Cheers,
Longman
next prev parent reply other threads:[~2019-02-14 22:05 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-13 22:00 [PATCH v4 0/3] locking/rwsem: Rwsem rearchitecture part 0 Waiman Long
2019-02-13 22:00 ` [PATCH v4 1/3] locking/rwsem: Remove arch specific rwsem files Waiman Long
2019-02-20 14:47 ` Will Deacon
2019-02-13 22:00 ` [PATCH v4 2/3] locking/rwsem: Remove rwsem-spinlock.c & use rwsem-xadd.c for all archs Waiman Long
2019-02-14 10:54 ` Geert Uytterhoeven
2019-02-14 11:12 ` Peter Zijlstra
2019-02-20 14:47 ` Will Deacon
2019-02-13 22:00 ` [PATCH v4 3/3] locking/rwsem: Optimize down_read_trylock() Waiman Long
2019-02-21 14:14 ` Will Deacon
2019-02-22 3:28 ` Waiman Long
2019-02-14 10:37 ` [PATCH v4 0/3] locking/rwsem: Rwsem rearchitecture part 0 Peter Zijlstra
2019-02-14 22:05 ` Waiman Long [this message]
2019-02-15 18:40 ` Will Deacon
2019-02-15 18:58 ` Waiman Long
2019-02-18 14:58 ` Will Deacon
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