linux-kernel - Re: [PATCH 3/7] perf_counter: ioctl(PERF_COUNTER_IOC

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] [day] [month] [year] [list]

Date:	Tue, 5 May 2009 21:31:09 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Paul Mackerras <paulus@...ba.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] perf_counter: ioctl(PERF_COUNTER_IOC_RESET)


* Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> On Tue, 2009-05-05 at 11:31 -0700, Corey Ashford wrote:
> > Hi Peter,
> > 
> > Peter Zijlstra wrote:
> > 
> > > +static void perf_counter_reset(struct perf_counter *counter)
> > > +{
> > > +	atomic_set(&counter->count, 0);
> > > +}
> > > +
> > 
> > 
> > Thanks for posting a patch for this issue.
> > 
> > As Ingo said, I think the hardware counter needs to be reset as well as 
> > the value saved in the perf_counter struct.
> > 
> 
> I don't think that's needed, we calculate a delta between prev_count and
> the current read and use that to increment counter->count. Therefore
> when we reset counter->count we should not need to touch the hardware
> counter.
> 
> However, I do think we need the below, first read the hardware counter
> to ensure that delta spoken of above is as close to zero as possible
> when we reset.
> 
> And update the user-page bits.
> 
> ---
> Index: linux-2.6/kernel/perf_counter.c
> ===================================================================
> --- linux-2.6.orig/kernel/perf_counter.c
> +++ linux-2.6/kernel/perf_counter.c
> @@ -1299,7 +1299,9 @@ static unsigned int perf_poll(struct fil
>  
>  static void perf_counter_reset(struct perf_counter *counter)
>  {
> +	(void)perf_counter_read(counter);
>  	atomic_set(&counter->count, 0);
> +	perf_counter_update_userpage(counter);
>  }

Mind sending a changelogged patch? Thanks,

	Ingo
--
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/