Re: [PATCH v2 3/4] tpm: reduce tpm_msleep() time in get_burstcount()

[Nayna Jain]

On 09/13/2017 06:30 AM, Jarkko Sakkinen wrote:
> On Wed, Sep 06, 2017 at 08:56:38AM -0400, Nayna Jain wrote:
> > Currently, get_burstcount() function sleeps for 5msec in a loop
> > before retrying for next query to burstcount. However, if it takes
> > lesser time for TPM to return, this 5 msec delay is longer
> > than necessary.
> >
> > This patch replaces the tpm_msleep time from 5msec to 1msec.
> >
> > After this change, performance on a TPM 1.2 with an 8 byte
> > burstcount for 1000 extends improved from ~10sec to ~9sec.
> >
> > Signed-off-by: Nayna Jain <nayna@xxxxxxxxxxxxxxxxxx>
> > Acked-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/char/tpm/tpm_tis_core.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> > index d1eab29cb447..d710bbc4608b 100644
> > --- a/drivers/char/tpm/tpm_tis_core.c
> > +++ b/drivers/char/tpm/tpm_tis_core.c
> > @@ -169,7 +169,7 @@ static int get_burstcount(struct tpm_chip *chip)
> >   		burstcnt = (value >> 8) & 0xFFFF;
> >   		if (burstcnt)
> >   			return burstcnt;
> > -		tpm_msleep(TPM_TIMEOUT);
> > +		tpm_msleep(1);
> >   	} while (time_before(jiffies, stop));
> >   	return -EBUSY;
> >   }
> > --
> > 2.13.3
> How did you pick 1 ms delay? Should there be a constant defining it?

As per ddwg input, the command may not take more than a few
microseconds. The minimum tpm_msleep() value is 1 msec, so we really
don't have a choice. Â(We're working on a patch set to lower this
value even more.)

Thanks & Regards,
    - Nayna

> /Jarkko