Date: Tue, 28 Jul 2015 10:18:03 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: What's left for 1.1.11 release? On Tue, Jul 28, 2015 at 04:09:38PM +0200, Jens Gustedt wrote: > Hello, > > Am Montag, den 27.07.2015, 23:40 -0400 schrieb Rich Felker: > > In principle the a_store issue affects all libc-internal __lock/LOCK > > uses, > > so this worries me since I assumed that UNLOCK had release consistency > for the __atomic implementation. It does. The problem is that it lacks acquire consistency, which we need in order to know whether to wake. > > and stdio locks too, but it's only been observed in malloc. > > Since there don't seem to be any performance-relevant uses of a_store > > that don't actually need the proper barrier, I think we have to just > > put an explicit barrier (lock orl $0,(%esp) or mfence) after the store > > and live with the loss of performance. > > How about using a xchg as instruction? This would perhaps "waste" a > register, but that sort of optimization should not be critical in the > vicinity of code that needs memory synchronization, anyhow. How is this better? My intent was to avoid incurring a read on the cache line that's being written and instead achieve the synchronization by poking at a cache line (the stack) that should not be shared. 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.