linux-kernel - Re: [PATCH 0/3] ARM Coresight: Enhance ETM tracing control

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Date:	Wed, 4 Dec 2013 16:12:56 -0500
From:	Adrien Vergé <adrienverge@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Russell King <linux@....linux.org.uk>,
	Ben Dooks <ben.dooks@...ethink.co.uk>,
	Will Deacon <will.deacon@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH 0/3] ARM Coresight: Enhance ETM tracing control

2013/12/4 Greg Kroah-Hartman <gregkh@...uxfoundation.org>:
> Your pid implementation is broken, see my other email about that :(

Thank you for your remarks on pid. I'll try to correct that.

> And again, what's wrong with the existing tracing functionalty that is
> processor agnostic?  Why can't we just delete this driver today and use
> the existing trace code?

As far as I know, the tracing functionality in
/sys/kernel/debug/tracing does not take advantage of ETM. ETM is a
dedicated hardware that greatly reduces tracing overhead. It only
exists on ARM platforms.

I understand using sysfs here is not the cleanest way. I patched my
kernel to meet my needs (trace a specific process or address range),
and I thought these small modifications could be useful -- until
bigger work is done to remove ETM control from sysfs.

Do you think it's worth correcting my patch (for pid namespaces) and
re-submitting it? Or should we wait for someone to port ETM tracing to
debugfs?

Thanks,

Adrien
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