linux-kernel - Re: [RFC][PATCH] perf_events: added new start/stop PMU callbacks

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:	Mon, 8 Feb 2010 18:21:46 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, paulus@...ba.org,
	davem@...emloft.net, fweisbec@...il.com, robert.richter@....com,
	perfmon2-devel@...ts.sf.net, eranian@...il.com
Subject: Re: [RFC][PATCH] perf_events: added new start/stop PMU callbacks

On Mon, Feb 8, 2010 at 5:30 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, 2010-02-08 at 17:06 +0200, Stephane Eranian wrote:
>>       In certain situations, the kernel may need to stop and start the
>>       same event rapidly. The current PMU callbacks do not distinguish
>>       between stop and release  (i.e., stop + free the resource). Thus,
>>       a counter may be released, then it will be immediately re-acquired.
>>       Event scheduling will again take place with no guarantee to assign
>>       the same counter. On some processors, this may event yield to failure
>>       to assign the event back due to competion between cores.
>>
>>       This patch is adding a new pair of callback to stop and restart a
>>       counter without actually release the underlying counter resource.
>>       On stop, the counter is stopped, its values saved and that's it.
>>       On start, the value is reloaded and counter is restarted (on x86,
>>       actual restart is delayed until perf_enable()).
>>
>>       Note this patch does not provide support for non-X86 PMU. This needs
>>       to be added.
>>
>>       Signed-off-by: Stephane Eranian <eranian@...gle.com>
>> --
>
> I think we can do this much easier by adding a list_head to
> hw_perf_event and make event_list into a proper list, then we can remove
> that funny loop on remove and instead move the event to a remove_list
> when there's a put_event_constraint() method and iterate that list on
> hw_perf_enable().

Not sure why it's easier. It saves memory for sure, but that problem
is independent of the issue I was trying to address.

>
> But before we do that, I think we need to look at the /* hardware */
> part of struct hw_perf_event, and make that arch specific, we've been
> growing that a lot lately and I don't think !x86 uses any of that.
>
It is clear it will need to grow much more to host non-counting features.
I have played with that myself a few weeks back. So, yes the saved state
needs to be arch specific.
--
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/