Date: Wed, 26 Jun 2013 14:07:49 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: "Yan, Zheng" <zheng.z.yan@intel.com>
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, eranian@google.com,
        andi@firstfloor.org
Subject: Re: [PATCH 0/7] perf, x86: Haswell LBR call stack support
Message-ID: <20130626120749.GH28407@twins.programming.kicks-ass.net>
References: <1372150039-15151-1-git-send-email-zheng.z.yan@intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1372150039-15151-1-git-send-email-zheng.z.yan@intel.com>
User-Agent: Mutt/1.5.21 (2012-12-30)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1473
Lines: 30

On Tue, Jun 25, 2013 at 04:47:12PM +0800, Yan, Zheng wrote:
> From: "Yan, Zheng" <zheng.z.yan@intel.com>
> 
> Haswell has a new feature that utilizes the existing Last Branch Record
> facility to record call chains. When the feature is enabled, function
> call will be collected as normal, but as return instructions are executed
> the last captured branch record is popped from the on-chip LBR registers.
> The LBR call stack facility can help perf to get call chains of progam
> without frame pointer. When perf tool requests PERF_SAMPLE_CALLCHAIN +
> PERF_SAMPLE_BRANCH_USER, this feature is dynamically enabled by default.
> This feature can be disabled/enabled through an attribute file in the cpu
> pmu sysfs directory.
> 
> The LBR call stack has following known limitations
>  1. Zero length calls are not filtered out by hardware
>  2. Exception handing such as setjmp/longjmp will have calls/returns not
>     match
>  3. Pushing different return address onto the stack will have calls/returns
>     not match
> 
> These patches are based upon tip/perf/core

These patches are also done wrong; the first patches should add HSW
support for the existing features. Only then should you do patches for
new fail^wfeatures.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/