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From: Vineet Gupta <Vineet.Gupta1@synopsys.com>
To: Peter Zijlstra <peterz@infradead.org>
CC: Andi Kleen <andi@firstfloor.org>,
        Alexey Brodkin <Alexey.Brodkin@synopsys.com>,
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Subject: Re: [RFC] perf: fix building for ARCv1
Thread-Topic: [RFC] perf: fix building for ARCv1
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Date: Mon, 19 Oct 2015 10:04:29 +0000
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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 agree - we can add that syscall trivially and use it based on build time feature
detection for atomics !