From: Vineet Gupta <Vineet.Gupta1@synopsys.com>
To: Peter Zijlstra <peterz@infradead.org>, Noam Camus <noamc@ezchip.com>
Cc: Andi Kleen <andi@firstfloor.org>,
Alexey Brodkin <Alexey.Brodkin@synopsys.com>,
Gilad Ben Yossef <giladb@ezchip.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-perf-users@vger.kernel.org"
<linux-perf-users@vger.kernel.org>,
"dvhart@linux.intel.com" <dvhart@linux.intel.com>,
"dsahern@gmail.com" <dsahern@gmail.com>,
"acme@redhat.com" <acme@redhat.com>
Subject: Re: [RFC] perf: fix building for ARCv1
Date: Tue, 20 Oct 2015 08:00:46 +0000 [thread overview]
Message-ID: <C2D7FE5348E1B147BCA15975FBA23075F44CB43D@IN01WEMBXA.internal.synopsys.com> (raw)
In-Reply-To: 20151019095157.GM3816@twins.programming.kicks-ass.net
On Monday 19 October 2015 03:22 PM, Peter Zijlstra wrote:
> On Mon, Oct 19, 2015 at 09:46:35AM +0000, Vineet Gupta wrote:
>> On ARC we could use the atomic EXchange to implement a user space only binary
>> semaphore - these atomic ops will be small duration so it is OK to spin wait for a
>> little bit. That's how the old pthread library worked for ARC w/o any atomic support.
> That has the obvious problem of lock-holder-preemption and the horrible
> performance issues that result from that.
>
> I think the syscall at least has deterministic behaviour, whereas that
> userspace spin loop has this abysmal worst case thing.
I don't have issue with adding the syscall per-se. But that comes with it's own
headaches of ABI change - more importantly it requires several things to match,
libc, kernel... It would be easier if change was confined to say perf.
Can we use existing syscall(s) - again this is what our good old pthread library
code did.
static void __pthread_acquire(int * spinlock)
{
int cnt = 0;
struct timespec tm;
READ_MEMORY_BARRIER();
while (testandset(spinlock)) { <---- atomic EXchange
if (cnt < 50) {
sched_yield();
cnt++;
} else {
tm.tv_sec = 0;
tm.tv_nsec = 2000001;
nanosleep(&tm, ((void *)0));
cnt = 0;
}
}
next prev parent reply other threads:[~2015-10-20 8:00 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1445088959-3058-1-git-send-email-abrodkin@synopsys.com>
2015-10-17 14:19 ` [RFC] perf: fix building for ARCv1 Vineet Gupta
2015-10-18 11:15 ` Alexey Brodkin
2015-10-18 23:14 ` Andi Kleen
2015-10-19 4:58 ` Vineet Gupta
2015-10-19 5:49 ` Andi Kleen
2015-10-19 9:28 ` Vineet Gupta
2015-10-19 9:35 ` Peter Zijlstra
2015-10-19 9:46 ` Vineet Gupta
2015-10-19 9:51 ` Peter Zijlstra
2015-10-19 10:04 ` Vineet Gupta
2015-10-20 8:00 ` Vineet Gupta [this message]
2015-10-20 10:11 ` Peter Zijlstra
2015-10-20 10:45 ` Vineet Gupta
2015-10-29 15:58 ` Alexey Brodkin
2015-10-30 6:19 ` Vineet Gupta
2016-02-03 16:20 ` Alexey Brodkin
[not found] ` <1454516455.2811.4.camel__10775.5710989752$1454516490$gmane$org@synopsys.com>
2016-02-04 4:13 ` Vineet Gupta
2016-02-05 11:18 ` Noam Camus
[not found] ` <20160205161027.GG28242@kernel.org>
2016-02-10 3:09 ` Vineet Gupta
2016-10-18 18:58 ` Vineet Gupta
2016-10-24 16:17 ` [PATCH-v2] ARC: syscall for userspace cmpxchg assist Vineet Gupta
2016-11-04 20:16 ` Vineet Gupta
2016-11-07 18:50 ` [PATCH] ARC: tweak semantics of " Vineet Gupta
2015-10-30 6:21 ` [RFC] perf: fix building for ARCv1 Vineet Gupta
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