Date: Mon, 30 Apr 2018 11:35:55 -0400 From: Rich Felker <dalias@...c.org> To: Patrick Oppenlander <patrick.oppenlander@...il.com> Cc: musl@...ts.openwall.com Subject: Re: Some questions On Mon, Apr 30, 2018 at 01:55:16PM +1000, Patrick Oppenlander wrote: > 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. I see. Is this an issue you've actually hit? I don't see any obvious way to make this decision at runtime that doesn't incur unwanted costs or failure modes, and I suspect we're spinning way too many times anyway even for SMP (i.e. the ideal solution might just be significantly reducing the # of spins). Rich
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.