From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Waiman Long <longman@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org,
linux-mips@vger.kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
sparclinux@vger.kernel.org, linux-riscv@lists.infradead.org,
linux-arch@vger.kernel.org, linux-s390@vger.kernel.org,
Davidlohr Bueso <dave@stgolabs.net>,
linux-c6x-dev@linux-c6x.org, linux-hexagon@vger.kernel.org,
x86@kernel.org, uclinux-h8-devel@lists.sourceforge.jp,
linux-xtensa@linux-xtensa.org, Arnd Bergmann <arnd@arndb.de>,
linux-um@lists.infradead.org, linux-m68k@lists.linux-m68k.org,
openrisc@lists.librecores.org, Borislav Petkov <bp@alien8.de>,
linux-arm-kernel@lists.infradead.org,
Tim Chen <tim.c.chen@linux.intel.com>,
linux-parisc@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org,
nios2-dev@lists.rocketboards.org,
Andrew Morton <akpm@linux-foundation.org>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v5 3/3] locking/rwsem: Optimize down_read_trylock()
Date: Fri, 22 Mar 2019 17:25:01 +0000 [thread overview]
Message-ID: <20190322172501.3nbjw6e2wqsaisgw@shell.armlinux.org.uk> (raw)
In-Reply-To: <20190322143008.21313-4-longman@redhat.com>
On Fri, Mar 22, 2019 at 10:30:08AM -0400, Waiman Long wrote:
> Modify __down_read_trylock() to optimize for an unlocked rwsem and make
> it generate slightly better code.
>
> Before this patch, down_read_trylock:
>
> 0x0000000000000000 <+0>: callq 0x5 <down_read_trylock+5>
> 0x0000000000000005 <+5>: jmp 0x18 <down_read_trylock+24>
> 0x0000000000000007 <+7>: lea 0x1(%rdx),%rcx
> 0x000000000000000b <+11>: mov %rdx,%rax
> 0x000000000000000e <+14>: lock cmpxchg %rcx,(%rdi)
> 0x0000000000000013 <+19>: cmp %rax,%rdx
> 0x0000000000000016 <+22>: je 0x23 <down_read_trylock+35>
> 0x0000000000000018 <+24>: mov (%rdi),%rdx
> 0x000000000000001b <+27>: test %rdx,%rdx
> 0x000000000000001e <+30>: jns 0x7 <down_read_trylock+7>
> 0x0000000000000020 <+32>: xor %eax,%eax
> 0x0000000000000022 <+34>: retq
> 0x0000000000000023 <+35>: mov %gs:0x0,%rax
> 0x000000000000002c <+44>: or $0x3,%rax
> 0x0000000000000030 <+48>: mov %rax,0x20(%rdi)
> 0x0000000000000034 <+52>: mov $0x1,%eax
> 0x0000000000000039 <+57>: retq
>
> After patch, down_read_trylock:
>
> 0x0000000000000000 <+0>: callq 0x5 <down_read_trylock+5>
> 0x0000000000000005 <+5>: xor %eax,%eax
> 0x0000000000000007 <+7>: lea 0x1(%rax),%rdx
> 0x000000000000000b <+11>: lock cmpxchg %rdx,(%rdi)
> 0x0000000000000010 <+16>: jne 0x29 <down_read_trylock+41>
> 0x0000000000000012 <+18>: mov %gs:0x0,%rax
> 0x000000000000001b <+27>: or $0x3,%rax
> 0x000000000000001f <+31>: mov %rax,0x20(%rdi)
> 0x0000000000000023 <+35>: mov $0x1,%eax
> 0x0000000000000028 <+40>: retq
> 0x0000000000000029 <+41>: test %rax,%rax
> 0x000000000000002c <+44>: jns 0x7 <down_read_trylock+7>
> 0x000000000000002e <+46>: xor %eax,%eax
> 0x0000000000000030 <+48>: retq
>
> By using a rwsem microbenchmark, the down_read_trylock() rate (with a
> load of 10 to lengthen the lock critical section) on a x86-64 system
> before and after the patch were:
>
> Before Patch After Patch
> # of Threads rlock rlock
> ------------ ----- -----
> 1 14,496 14,716
> 2 8,644 8,453
> 4 6,799 6,983
> 8 5,664 7,190
>
> On a ARM64 system, the performance results were:
>
> Before Patch After Patch
> # of Threads rlock rlock
> ------------ ----- -----
> 1 23,676 24,488
> 2 7,697 9,502
> 4 4,945 3,440
> 8 2,641 1,603
>
> For the uncontended case (1 thread), the new down_read_trylock() is a
> little bit faster. For the contended cases, the new down_read_trylock()
> perform pretty well in x86-64, but performance degrades at high
> contention level on ARM64.
So, 70% for 4 threads, 61% for 4 threads - does this trend
continue tailing off as the number of threads (and cores)
increase?
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up
next prev parent reply other threads:[~2019-03-22 17:25 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-22 14:30 [PATCH v5 0/3] locking/rwsem: Rwsem rearchitecture part 0 Waiman Long
2019-03-22 14:30 ` [PATCH v5 1/3] locking/rwsem: Remove arch specific rwsem files Waiman Long
2019-03-22 17:01 ` Linus Torvalds
2019-03-22 17:23 ` Waiman Long
2019-03-22 19:30 ` Davidlohr Bueso
2019-03-22 20:27 ` Waiman Long
2019-03-22 14:30 ` [PATCH v5 2/3] locking/rwsem: Remove rwsem-spinlock.c & use rwsem-xadd.c for all archs Waiman Long
2019-03-22 17:07 ` Linus Torvalds
2019-03-22 14:30 ` [PATCH v5 3/3] locking/rwsem: Optimize down_read_trylock() Waiman Long
2019-03-22 17:08 ` Linus Torvalds
2019-03-22 17:25 ` Russell King - ARM Linux admin [this message]
2019-03-22 17:41 ` Waiman Long
2019-03-25 15:25 ` Christophe Leroy
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