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Message-ID: <CAEg67GkYqBsFYLm0dUM27BbkSuyADifYAiTU463MunBA+=QB9g@mail.gmail.com>
Date: Mon, 30 Apr 2018 13:55:16 +1000
From: Patrick Oppenlander <patrick.oppenlander@...il.com>
To: musl@...ts.openwall.com
Subject: Re: Some questions
On Mon, Apr 30, 2018 at 1:16 PM, Rich Felker <dalias@...c.org> wrote:
> On Mon, Apr 30, 2018 at 12:52:06PM +1000, Patrick Oppenlander wrote:
>> - Is there a way that spinlocks could be disabled or bypassed on
>> uniprocessor systems?
>
> Whether locks are needed is a matter of whether there are multiple
> threads, not whether it's uniprocessor or multiprocessor. For some
> things where it's likely to matter (stdio, malloc, some other
> internals), locks are already optimized out when there is only one
> thread. In other cases it was deemed either too costly/difficult or
> irrelevant to overall performance.
I was talking about the case of a uniprocessor system running a multi
theaded process.
In that case the "spin" part of spinlock just burns time & electrons.
The "lock" part obviously can't be omitted. Calling straight through
to the kernel is the most efficient thing to do.
Patrick
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