linux-kernel - Re: [PATCH] perf: Store active software events in a hashlist

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 06 Apr 2010 17:27:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH] perf: Store active software events in a hashlist

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.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/