perf: Store active software events in a hashlist
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From: Peter Zijlstra on 7 Apr 2010 08:00 On Wed, 2010-04-07 at 13:52 +0200, Frederic Weisbecker wrote: > On Wed, Apr 07, 2010 at 11:02:26AM +0200, Peter Zijlstra wrote: > > On Mon, 2010-04-05 at 16:08 +0200, Frederic Weisbecker wrote: > > > +#define SWEVENT_HLIST_BITS 8 > > > +#define SWEVENT_HLIST_SIZE ((1 << (SWEVENT_HLIST_BITS + 1)) - 1) > > > > That seems to result in 9 bits worth, doesn't it? > > > Oh right, I was confused, will zapp the + 1. > Also, what you're computing seems to be a mask, not a size So with BITS = 8, you want SIZE = 1<<BITS = 256 MASK = SIZE-1 = 255 right? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Frederic Weisbecker on 7 Apr 2010 08:00 On Wed, Apr 07, 2010 at 11:02:26AM +0200, Peter Zijlstra wrote: > On Mon, 2010-04-05 at 16:08 +0200, Frederic Weisbecker wrote: > > +#define SWEVENT_HLIST_BITS 8 > > +#define SWEVENT_HLIST_SIZE ((1 << (SWEVENT_HLIST_BITS + 1)) - 1) > > That seems to result in 9 bits worth, doesn't it? Oh right, I was confused, will zapp the + 1. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Frederic Weisbecker on 7 Apr 2010 08:10 On Wed, Apr 07, 2010 at 01:56:45PM +0200, Peter Zijlstra wrote: > On Wed, 2010-04-07 at 13:52 +0200, Frederic Weisbecker wrote: > > On Wed, Apr 07, 2010 at 11:02:26AM +0200, Peter Zijlstra wrote: > > > On Mon, 2010-04-05 at 16:08 +0200, Frederic Weisbecker wrote: > > > > +#define SWEVENT_HLIST_BITS 8 > > > > +#define SWEVENT_HLIST_SIZE ((1 << (SWEVENT_HLIST_BITS + 1)) - 1) > > > > > > That seems to result in 9 bits worth, doesn't it? > > > > > > Oh right, I was confused, will zapp the + 1. > > > > Also, what you're computing seems to be a mask, not a size > > So with BITS = 8, you want > SIZE = 1<<BITS = 256 > MASK = SIZE-1 = 255 > > right? Oh right... damn I suck in maths... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Frederic Weisbecker on 7 Apr 2010 08:10 On Wed, Apr 07, 2010 at 01:58:20PM +0200, Peter Zijlstra wrote: > On Wed, 2010-04-07 at 13:56 +0200, Frederic Weisbecker wrote: > > > > > > > > So looks good, altough I think we want to do that online/hotplug thing. > > > > > > That would let us allocate on online cpus instead of possibles? Yeah right. > > Right, so if you want to go this route (and not simply embed it in the > percpu data), the complication I thought of is that you want the > refcount on offline cpus but not the allocation, since its very hard to > reconstruct the number of events that had event->cpu == -1. Ok, right I can do that. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Peter Zijlstra on 7 Apr 2010 08:10
On Wed, 2010-04-07 at 13:58 +0200, Frederic Weisbecker wrote: > On Wed, Apr 07, 2010 at 11:04:53AM +0200, Peter Zijlstra wrote: > > On Tue, 2010-04-06 at 17:27 +0200, Peter Zijlstra wrote: > > > On Mon, 2010-04-05 at 16:08 +0200, Frederic Weisbecker wrote: > > > > Each time a software event triggers, we need to walk through > > > > the entire list of events from the current cpu and task contexts > > > > to retrieve a running perf event that matches. > > > > We also need to check a matching perf event is actually counting. > > > > > > > > This walk is wasteful and makes the event fast path scaling > > > > down with a growing number of events running on the same > > > > contexts. > > > > > > > > To solve this, we store the running perf events in a hashlist to > > > > get an immediate access to them against their type:event_id when > > > > they trigger. > > > > > > So we have a hash-table per-cpu, each event takes a ref on the hash > > > table, when the thing is empty we free it. > > > > > > When the event->cpu == -1 (all cpus) we take a ref on all possible cpu's > > > hash-table (should be online I figure, but that requires adding a > > > hotplug handler). > > > > > > Then on event enable/disable we actually add the event to the hash-table > > > belonging to the cpu the event/task gets scheduled on, since each event > > > can only ever be active on one cpu. > > > > > > Right? > > > > > > So looks good, altough I think we want to do that online/hotplug thing. > > > > Alternatively, you can simply but the hash table into the per-cpu > > structure and not allocate it, its only a single page (half a page if > > you use 32bit or actually use 8 bits. > > > As you prefer. This would indeed make it more simple, but that would also > make these pages unused most of the time. True I suppose,.. have a go at that hotplug stuff, the only thing I worried about was that refcount stuff getting rather ugly. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |