Messages in this thread | | | Subject | Re: [PATCH 1/4, v2] x86: enlightenment for ticket spin locks - base implementation | From | Peter Zijlstra <> | Date | Wed, 30 Jun 2010 11:11:56 +0200 |
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On Wed, 2010-06-30 at 10:00 +0100, Jan Beulich wrote: > >>> On 30.06.10 at 10:05, Peter Zijlstra <peterz@infradead.org> wrote: > > On Tue, 2010-06-29 at 15:31 +0100, Jan Beulich wrote: > >> Add optional (alternative instructions based) callout hooks to the > >> contended ticket lock and the ticket unlock paths, to allow hypervisor > >> specific code to be used for reducing/eliminating the bad effects > >> ticket locks have on performance when running virtualized. > > > > Uhm, I'd much rather see a single alternative implementation, not a > > per-hypervisor lock implementation. > > How would you imaging this to work? I can't see how the mechanism > could be hypervisor agnostic. Just look at the Xen implementation > (patch 2) - do you really see room for meaningful abstraction there?
I tried not to, it made my eyes bleed..
But from what I hear all virt people are suffering from spinlocks (and fair spinlocks in particular), so I was thinking it'd be a good idea to get all interested parties to collaborate on one. Fragmentation like this hardly ever works out well.
> Not the least that not every hypervisor may even have a way to > poll for events (like Xen does), in which case a simple yield may be > needed instead.
No idea what you're talking about, I think you assume I actually know something about Xen or virt..
> >> For the moment, this isn't intended to be used together with pv-ops, > >> but this is just to simplify initial integration. The ultimate goal > >> for this should still be to replace pv-ops spinlocks. > > > > So why not start by removing that? > > Because I wouldn't get around to test it within the time constraints > I have?
I'd say that removing basically dead code (the paravirt spinlocks) the code you'd be changing was easier to follow and thus your patches would be done quicker?
> >> +#define ALTERNATIVE_TICKET_LOCK \ > > > > But but but, the alternative isn't a ticket lock..!? > > ??? Of course it is.
Ah, right, after looking a bit more at patch 2 I see you indeed implement a ticket like lock. Although why you need both a ticket and a FIFO list is beyond me.
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