linux-kernel - RE: [patch] x86, perf_counter, bts: add bts to perf

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:	Fri, 07 Aug 2009 15:05:58 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	"Metzger, Markus T" <markus.t.metzger@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"hpa@...or.com" <hpa@...or.com>,
	"markus.t.metzger@...il.com" <markus.t.metzger@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [patch] x86, perf_counter, bts: add bts to perf_counter

On Fri, 2009-08-07 at 13:18 +0100, Metzger, Markus T wrote:

> >Right, what I'm worried about though is the BTS overload scenario.
> >Normally when we'd create more counters than we'd have hardware for we'd
> >simply time share the stuff.
> >
> >However BTS now has a second class fallback for period==1 which
> >complicates all this because it will likely not generate consistent
> >results.
> >
> >So I was thinking that _if_ the hardware supports BTS we'd not do the
> >fallback to generic bits if event == HW_BRANCH_INST && period == 1.
> >
> >I agree on the period > 1 using the generic counters.
> 
> 
> OK, that makes sense.
> 
> So I'll still check for sample_period=1 but when I fail to acquire BTS, I don't
> fall back to the generic counter and return an error instead.
> 
> Is that it?

Yeah, something like that, simply return -EBUSY/-EAGAIN or so.

However I'd look into adding something to intel_pmu_init() which would
set intel_bts_available to 1 when the CPU should support BTS, that'll
ease the reserve_bts_hardware() error case and help with allowing this
fallback as well.



--
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/