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[174.227.146.178]) by smtp.gmail.com with ESMTPSA id 92sm5508111qtc.97.2019.03.22.13.13.53 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 22 Mar 2019 13:13:57 -0700 (PDT) Subject: Re: [PATCH 2/4] glibc: sched_getcpu(): use rseq cpu_id TLS on Linux To: Mathieu Desnoyers , Carlos O'Donell Cc: Florian Weimer , Joseph Myers , Szabolcs Nagy , libc-alpha@sourceware.org, Thomas Gleixner , Ben Maurer , Peter Zijlstra , "Paul E. McKenney" , Boqun Feng , Will Deacon , Dave Watson , Paul Turner , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org References: <20190212194253.1951-1-mathieu.desnoyers@efficios.com> <20190212194253.1951-3-mathieu.desnoyers@efficios.com> From: Carlos O'Donell Message-ID: Date: Fri, 22 Mar 2019 16:13:52 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.3 MIME-Version: 1.0 In-Reply-To: <20190212194253.1951-3-mathieu.desnoyers@efficios.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/12/19 2:42 PM, Mathieu Desnoyers wrote: > When available, use the cpu_id field from __rseq_abi on Linux to > implement sched_getcpu(). Fall-back on the vgetcpu vDSO if unavailable. > > Benchmarks: > > x86-64: Intel E5-2630 v3@2.40GHz, 16-core, hyperthreading This patch looks good to me for master, but is blocked on patch 1/4 being reworked. Reviewed-by: Carlos O'Donell > glibc sched_getcpu(): 13.7 ns (baseline) > glibc sched_getcpu() using rseq: 2.5 ns (speedup: 5.5x) > inline load cpuid from __rseq_abi TLS: 0.8 ns (speedup: 17.1x) > > Signed-off-by: Mathieu Desnoyers > CC: Carlos O'Donell > CC: Florian Weimer > CC: Joseph Myers > CC: Szabolcs Nagy > CC: Thomas Gleixner > CC: Ben Maurer > CC: Peter Zijlstra > CC: "Paul E. McKenney" > CC: Boqun Feng > CC: Will Deacon > CC: Dave Watson > CC: Paul Turner > CC: libc-alpha@sourceware.org > CC: linux-kernel@vger.kernel.org > CC: linux-api@vger.kernel.org > --- > sysdeps/unix/sysv/linux/sched_getcpu.c | 25 +++++++++++++++++++++++-- > 1 file changed, 23 insertions(+), 2 deletions(-) > > diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c > index fb0d317f83..8bfb03778b 100644 > --- a/sysdeps/unix/sysv/linux/sched_getcpu.c > +++ b/sysdeps/unix/sysv/linux/sched_getcpu.c > @@ -24,8 +24,8 @@ > #endif > #include > > -int > -sched_getcpu (void) > +static int > +vsyscall_sched_getcpu (void) OK. > { > #ifdef __NR_getcpu > unsigned int cpu; > @@ -37,3 +37,24 @@ sched_getcpu (void) > return -1; > #endif > } > + > +#ifdef __NR_rseq > +#include > + > +extern __attribute__ ((tls_model ("initial-exec"))) > +__thread volatile struct rseq __rseq_abi; OK. > + > +int > +sched_getcpu (void) > +{ > + int cpu_id = __rseq_abi.cpu_id; > + > + return cpu_id >= 0 ? cpu_id : vsyscall_sched_getcpu (); OK. Impressive :-) > +} > +#else > +int > +sched_getcpu (void) > +{ > + return vsyscall_sched_getcpu (); OK. > +} > +#endif > -- Cheers, Carlos.