Re: [PATCH] perf: add 'perf bench syscall'

[Andy Lutomirski]

On Jun 21, 2016 7:55 AM, "Josh Poimboeuf" <jpoimboe@xxxxxxxxxx> wrote:
>
> On Mon, Jun 20, 2016 at 12:16:22PM -0700, Andy Lutomirski wrote:
> > On Mon, Jun 20, 2016 at 11:00 AM, Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:
> >
> > >
> > > From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> > > Subject: [PATCH] perf: add 'perf bench syscall'
> > >
> > > Add a basic 'perf bench syscall' benchmark which does a getppid() system
> > > call in a tight loop.
> > >
> >
> > My one suggestion would be to use a different syscall than getppid(),
> > as getppid() can have unusual performance characteristics on kernels
> > with pid namespaces enabled.  I'm a fan of prctl(-1, 0, 0, 0, 0).
>
> Hm, can you elaborate on the unusual performance characteristics of
> getppid()?  The code seems pretty minimal.

task_this_vnr -> pid_vnr -> pid_nr_ns

There's probably something better than prctl, though.

--Andy