From: Julien Grall <julien.grall@linaro.org>
To: Ian Campbell <Ian.Campbell@citrix.com>
Cc: xen-devel@lists.xenproject.org, tim@xen.org,
stefano.stabellini@citrix.com
Subject: Re: [PATCH 2/4] xen/arm: Implement a dummy Performance Monitor for ARM32
Date: Fri, 02 May 2014 13:41:06 +0100 [thread overview]
Message-ID: <53639262.2090208@linaro.org> (raw)
In-Reply-To: <1399028472.32736.39.camel@kazak.uk.xensource.com>
On 05/02/2014 12:01 PM, Ian Campbell wrote:
> On Thu, 2014-04-24 at 23:45 +0100, Julien Grall wrote:
>> XSA-93 (commit 0b18220 "xen/arm: Don't let guess access to Debug and Performance
>> Monitor registers") disable Performance Monitor.
>>
>> When CONFIG_PERF_EVENTS is enabled in the Linux Kernel, regardless the
>> ID_DFR0 (which tell if Perfomance Monitors Extension is implemented) the
>> kernel will try to access to PMCR.
>>
>> Therefore we tell the guest we have 0 counters. Unfortunately we must always
>> support PMCCNTR (the cycle counter): we just RAZ/WI for all PM register,
>> which doesn't crash the kernel at least.
>
> How often does this trap occur in practice? Once at start of day? Only
> if you run perf? Or on every guest context switch? (obviously the last
> one would be bad...)
There is few calls to the perf registers during the boot (when Linux is
compiled with CONFIG_PERF_EVENTS=y).
I didn't see any usage during guest context switch. I haven't try perf.
Regards,
--
Julien Grall
next prev parent reply other threads:[~2014-05-02 12:41 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-24 22:45 [PATCH 0/4] xen/arm32: Follow-up XSA-93 Julien Grall
2014-04-24 22:45 ` [PATCH 1/4] xen/arm: Add missing newline after commit 60f7376 Julien Grall
2014-05-02 12:58 ` Ian Campbell
2014-05-02 12:59 ` Julien Grall
2014-04-24 22:45 ` [PATCH 2/4] xen/arm: Implement a dummy Performance Monitor for ARM32 Julien Grall
2014-05-02 11:01 ` Ian Campbell
2014-05-02 12:41 ` Julien Grall [this message]
2014-06-13 12:02 ` Ian Campbell
2014-04-24 22:45 ` [PATCH 3/4] xen/arm: Implement a dummy debug monitor " Julien Grall
2014-05-02 11:09 ` Ian Campbell
2014-05-02 12:53 ` Julien Grall
2014-05-02 13:14 ` Ian Campbell
2014-05-02 13:29 ` Julien Grall
2014-06-13 12:02 ` Ian Campbell
2014-06-14 17:16 ` Julien Grall
2014-05-02 13:26 ` Ian Campbell
2014-05-02 13:39 ` Julien Grall
2014-05-02 14:18 ` Ian Campbell
2014-05-02 14:22 ` Julien Grall
2014-05-02 15:17 ` Ian Campbell
2014-04-24 22:45 ` [PATCH 4/4] xen/arm: Add some useful debug in coprocessor trapping Julien Grall
2014-05-02 11:12 ` Ian Campbell
2014-05-02 12:58 ` Julien Grall
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