From: Andi Kleen <andi@firstfloor.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Florian Weimer <fweimer@redhat.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Andrew Morton <akpm@linux-foundation.org>,
Russell King <linux@arm.linux.org.uk>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-api <linux-api@vger.kernel.org>,
Paul Turner <pjt@google.com>, Andrew Hunter <ahh@google.com>,
Andy Lutomirski <luto@amacapital.net>,
Andi Kleen <andi@firstfloor.org>,
Dave Watson <davejwatson@fb.com>, Chris Lameter <cl@linux.com>,
Ben Maurer <bmaurer@fb.com>, rostedt <rostedt@goodmis.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Josh Triplett <josh@joshtriplett.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Michael Kerrisk <mtk.manpages@gmail.com>,
Boqun Feng <boqun.feng@gmail.com>
Subject: Re: [RFC PATCH v6 1/5] Thread-local ABI system call: cache CPU number of running thread
Date: Thu, 7 Apr 2016 13:22:32 -0700 [thread overview]
Message-ID: <20160407202232.GF9407@two.firstfloor.org> (raw)
In-Reply-To: <1025228632.49344.1460054592801.JavaMail.zimbra@efficios.com>
> One basic use of cpu id cache is to speed up the sched_getcpu(3)
> implementation in glibc. This is why I'm proposing it as a stand-alone
I don't think rseq is needed for faster getcpu.
User space has to be able handle stale return values anyways, as it
has no way to lock itself to a cpu while it is using the return value.
So it can be only a hint.
The original version of getcpu just had a jiffies based cache. The CPU
value was valid up to a jiffie (the next time jiffie changes), and then it
gets looked up again.
Processes are unlikely to switch CPUs more often than a jiffie, so it's
good enough as a hint.
This doesn't need any new kernel interfaces at all because jiffies is already
exported to the vdso.
It just needs a new entry point into the vdso that handles the jiffie
check.
-Andi
next prev parent reply other threads:[~2016-04-07 20:22 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-04 17:01 [RFC PATCH v6 0/5] Thread-local ABI system call (CPU number cache) Mathieu Desnoyers
2016-04-04 17:01 ` [RFC PATCH v6 1/5] Thread-local ABI system call: cache CPU number of running thread Mathieu Desnoyers
2016-04-04 17:11 ` H. Peter Anvin
2016-04-04 19:46 ` Mathieu Desnoyers
2016-04-04 20:48 ` Mathieu Desnoyers
2016-04-05 16:02 ` Florian Weimer
2016-04-05 16:47 ` Peter Zijlstra
2016-04-07 9:01 ` Florian Weimer
2016-04-07 10:31 ` Peter Zijlstra
2016-04-07 10:39 ` Florian Weimer
2016-04-07 11:19 ` Peter Zijlstra
2016-04-07 12:03 ` Florian Weimer
2016-04-07 12:25 ` Peter Zijlstra
2016-04-07 12:37 ` Florian Weimer
2016-04-07 15:59 ` Mathieu Desnoyers
2016-04-07 12:34 ` Mathieu Desnoyers
2016-04-07 16:39 ` Linus Torvalds
2016-04-07 16:46 ` Andy Lutomirski
2016-04-07 16:50 ` Florian Weimer
2016-04-07 16:59 ` Linus Torvalds
2016-04-07 16:52 ` Linus Torvalds
2016-04-07 18:43 ` Mathieu Desnoyers
2016-04-07 20:22 ` Andi Kleen [this message]
2016-04-07 20:55 ` Mathieu Desnoyers
2016-04-07 10:40 ` Florian Weimer
2016-04-04 17:01 ` [RFC PATCH v6 2/5] Thread-local ABI cpu_id: ARM resume notifier Mathieu Desnoyers
2016-04-04 17:01 ` [RFC PATCH v6 3/5] Thread-local ABI: wire up ARM system call Mathieu Desnoyers
2016-04-04 17:01 ` [RFC PATCH v6 4/5] Thread-local ABI cpu_id: x86 32/64 resume notifier Mathieu Desnoyers
2016-04-04 17:01 ` [RFC PATCH v6 5/5] Thread-local ABI: wire up x86 32/64 system call Mathieu Desnoyers
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