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Date:   Thu, 4 Feb 2021 21:20:20 +1100
From:   Balbir Singh <bsingharora@gmail.com>
To:     Weiping Zhang <zwp10758@gmail.com>
Cc:     sblbir@amazon.com, davem@davemloft.net,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH v2] taskstats: add /proc/taskstats to fetch pid/tgid
 status
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On Sun, Jan 31, 2021 at 05:16:47PM +0800, Weiping Zhang wrote:
> On Wed, Jan 27, 2021 at 7:13 PM Balbir Singh <bsingharora@gmail.com> wrote:
> >
> > On Fri, Jan 22, 2021 at 10:07:50PM +0800, Weiping Zhang wrote:
> > > Hello Balbir Singh,
> > >
> > > Could you help review this patch, thanks
> > >
> > > On Mon, Dec 28, 2020 at 10:10 PM Weiping Zhang <zwp10758@gmail.com> wrote:
> > > >
> > > > Hi David,
> > > >
> > > > Could you help review this patch ?
> > > >
> > > > thanks
> > > >
> > > > On Fri, Dec 18, 2020 at 1:24 AM Weiping Zhang
> > > > <zhangweiping@didiglobal.com> wrote:
> > > > >
> > > > > If a program needs monitor lots of process's status, it needs two
> > > > > syscalls for every process. The first one is telling kernel which
> > > > > pid/tgid should be monitored by send a command(write socket) to kernel.
> > > > > The second one is read the statistics by read socket. This patch add
> > > > > a new interface /proc/taskstats to reduce two syscalls to one ioctl.
> > > > > The user just set the target pid/tgid to the struct taskstats.ac_pid,
> > > > > then kernel will collect statistics for that pid/tgid.
> > > > >
> > > > > Signed-off-by: Weiping Zhang <zhangweiping@didiglobal.com>
> >
> > Could you elaborate on the overhead your seeing for the syscalls? I am not
> > in favour of adding new IOCTL's.
> >
> > Balbir Singh.
> 
> Hello Balbir Singh,
> 
> Sorry for late reply,
> 
> I do a performance test between netlink mode and ioctl mode,
> monitor 1000 and 10000 sleep processes,
> the netlink mode cost more time than ioctl mode, that is to say
> ioctl mode can save some cpu resource and has a quickly reponse
> especially when monitor lot of process.
> 
> proccess-count    netlink         ioctl
> ---------------------------------------------
> 1000              0.004446851     0.001553733
> 10000             0.047024986     0.023290664
> 
> you can get the test demo code from the following link
> https://github.com/dublio/tools/tree/master/c/taskstat
>

Let me try it out, I am opposed to adding the new IOCTL interface
you propose. How frequently do you monitor this data and how much
time in spent in making decision on the data? I presume the data
mentioned is the cost per call in seconds?

Balbir Singh