Re: [PATCH 2/3] tpm: reduce poll sleep time between send() and recv() in tpm_transmit()

From: Jarkko Sakkinen
Date: Tue Mar 06 2018 - 06:06:24 EST


On Mon, 2018-03-05 at 14:07 -0500, Mimi Zohar wrote:
> On Mon, 2018-03-05 at 20:01 +0200, Jarkko Sakkinen wrote:
> > On Mon, Mar 05, 2018 at 12:56:33PM +0200, Jarkko Sakkinen wrote:
> > > On Fri, Mar 02, 2018 at 12:26:35AM +0530, Nayna Jain wrote:
> > > >
> > > >
> > > > On 03/01/2018 02:52 PM, Jarkko Sakkinen wrote:
> > > > > On Wed, Feb 28, 2018 at 02:18:27PM -0500, Nayna Jain wrote:
> > > > > > In tpm_transmit, after send(), the code checks for status in a loop
> > > > >
> > > > > Maybe cutting hairs now but please just use the actual function name
> > > > > instead of send(). Just makes the commit log more useful asset.
> > > >
> > > > Sure, will do.
> > > > >
> > > > > > - tpm_msleep(TPM_TIMEOUT);
> > > > > > + tpm_msleep(TPM_TIMEOUT_POLL);
> > > > >
> > > > > What about just calling schedule()?
> > > >
> > > > I'm not sure what you mean by "schedule()". Are you suggesting instead
> > > > of
> > > > using usleep_range(), using something with an even finer grain
> > > > construct?
> > > >
> > > > Thanks & Regards,
> > > > - Nayna
> > >
> > > kernel/sched/core.c
> >
> > The question I'm trying ask to is: is it better to sleep such a short
> > time or just ask scheduler to schedule something else after each
> > iteration?
>
> I still don't understand why scheduling some work would be an
> improvement. We still need to loop, testing for the TPM command to
> complete.
>
> According to the schedule_hrtimeout_range() function comment,
> schedule_hrtimeout_range() is both power and performance friendly.
> What we didn't realize is that the hrtimer *uses* the maximum range
> to calculate the sleep time, but *may* return earlier based on the
> minimum time.
>
> This patch minimizes the tpm_msleep(). The subsequent patch in this
> patch set shows that 1 msec isn't fine enough granularity. I still
> think calling usleep_range() is the right solution, but it needs to be
> at a finer granularity than tpm_msleep() provides.
>
> Mimi

We can move to usleep_range() in call sites where it makes sense instead
of adjusting tpm_msleep() implementation...

/Jarkko