Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Mon, 28 Jun 2021 15:29:05 +0800
From:   Leo Yan <leo.yan@linaro.org>
To:     Yang Jihong <yangjihong1@huawei.com>
Cc:     john.garry@huawei.com, will@kernel.org, mathieu.poirier@linaro.org,
        peterz@infradead.org, mingo@redhat.com, acme@kernel.org,
        mark.rutland@arm.com, alexander.shishkin@linux.intel.com,
        jolsa@redhat.com, namhyung@kernel.org, james.clark@arm.com,
        andre.przywara@arm.com, linux-arm-kernel@lists.infradead.org,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] perf arm-spe: Fix incorrect sample timestamp in perf
 script
Message-ID: <20210628072905.GB200044@leoy-ThinkPad-X240s>
References: <20210626032115.16742-1-yangjihong1@huawei.com>
 <20210628014953.GA163942@leoy-ThinkPad-X240s>
 <75dac5f8-9c82-0db1-d362-44289dcaa206@huawei.com>
 <20210628040716.GC163942@leoy-ThinkPad-X240s>
 <2af84c69-8528-9c4a-f666-2dd660bcd966@huawei.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <2af84c69-8528-9c4a-f666-2dd660bcd966@huawei.com>
Precedence: bulk

On Mon, Jun 28, 2021 at 02:30:56PM +0800, Yang Jihong wrote:
> Hello Leo,
> 
> On 2021/6/28 12:07, Leo Yan wrote:
> > On Mon, Jun 28, 2021 at 11:45:07AM +0800, Yang Jihong wrote:
> > 
> > [...]
> > 
> > > The timestamp does not match. Each timestamp has a difference of
> > > 213.98296702 seconds. Is the command I executed wrong?
> > 
> > I don't understand what's your meaning "a difference of 213.98296702
> > seconds".
> > 
> > But let me give an explaination with your below examples.  You could
> > the command "perf script" outputs the timestamp 314938.859071370 which
> > is the kernel's timestamp, if using the command "perf script -D", it
> > outputs the value 31515284203839 which is the Arch timer's raw counter
> > value.
> > 
> > In theory, the arch timer's counter is enabled at the very early
> > time before kernel's booting (e.g. bootloaders, UEFI, etc...).  So for
> > the kernel's timestamp, it should calibrate the timestamp and reduce
> > the offset prior to the kernel's booting.  I think this is the reason
> > why you observed 213.98296702 seconds difference (if compared with
> > your own patch?)
> > 
> > If still see any issue, please let me know.  Thanks a lot for the
> > testing!
> > 
> Thanks for the very detailed explanation.
> To keep the correct relative time sequence between events in SPE and other
> events, we should use kernel timestamp instead of arch time. Therefore, we
> need to calibrate the time. Is this correct?

Yes, correct!