Re: [PATCH v3 2/5] tpm: ignore burstcount to improve tpm_tis send() performance

[Nayna Jain]

On 10/10/2017 08:34 PM, Jarkko Sakkinen wrote:
> On Wed, Oct 04, 2017 at 06:29:21AM -0400, Nayna Jain wrote:
> > The TPM burstcount status indicates the number of bytes that can
> > be sent to the TPM without causing bus wait states.  Effectively,
> > it is the number of empty bytes in the command FIFO. Further,
> > some TPMs have a static burstcount, when the value remains zero
> > until the entire FIFO is empty.
> >
> > This patch optimizes the tpm_tis_send_data() function by checking
> > the burstcount only once. And if the burstcount is valid, it writes
> > all the bytes at once, permitting wait states. The performance of a
> > 34 byte extend on a TPM 1.2 with an 8 byte burstcount improved from
> > 41msec to 14msec.
> >
> > After this change, performance on a TPM 1.2 with an 8 byte
> > burstcount for 1000 extends improved from ~41sec to ~14sec.
> >
> > Suggested-by: Ken Goldman <kgold@xxxxxxxxxxxxxxxxxx> in
> > conjunction with the TPM Device Driver work group.
> > Signed-off-by: Nayna Jain <nayna@xxxxxxxxxxxxxxxxxx>
> > Acked-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/char/tpm/tpm_tis_core.c | 42 ++++++++++++++++-------------------------
> >   1 file changed, 16 insertions(+), 26 deletions(-)
> >
> > diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> > index b33126a35694..8da425e1783f 100644
> > --- a/drivers/char/tpm/tpm_tis_core.c
> > +++ b/drivers/char/tpm/tpm_tis_core.c
> > @@ -316,7 +316,6 @@ static int tpm_tis_send_data(struct tpm_chip *chip, u8 *buf, size_t len)
> >   {
> >   	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
> >   	int rc, status, burstcnt;
> > -	size_t count = 0;
> >   	bool itpm = priv->flags & TPM_TIS_ITPM_WORKAROUND;
> >   
> >   	status = tpm_tis_status(chip);
> > @@ -330,35 +329,26 @@ static int tpm_tis_send_data(struct tpm_chip *chip, u8 *buf, size_t len)
> >   		}
> >   	}
> >   
> > -	while (count < len - 1) {
> > -		burstcnt = get_burstcount(chip);
> > -		if (burstcnt < 0) {
> > -			dev_err(&chip->dev, "Unable to read burstcount\n");
> > -			rc = burstcnt;
> > -			goto out_err;
> > -		}
> > -		burstcnt = min_t(int, burstcnt, len - count - 1);
> > -		rc = tpm_tis_write_bytes(priv, TPM_DATA_FIFO(priv->locality),
> > -					 burstcnt, buf + count);
> > -		if (rc < 0)
> > -			goto out_err;
> > +	/*
> > +	 * Get the initial burstcount to ensure TPM is ready to
> > +	 * accept data.
> > +	 */
> > +	burstcnt = get_burstcount(chip);
> > +	if (burstcnt < 0) {
> > +		dev_err(&chip->dev, "Unable to read burstcount\n");
> > +		rc = burstcnt;
> > +		goto out_err;
> > +	}
> >   
> > -		count += burstcnt;
> > +	burstcnt = len - 1;
> >   
> > -		if (wait_for_tpm_stat(chip, TPM_STS_VALID, chip->timeout_c,
> > -					&priv->int_queue, false) < 0) {
> > -			rc = -ETIME;
> > -			goto out_err;
> > -		}
> > -		status = tpm_tis_status(chip);
> > -		if (!itpm && (status & TPM_STS_DATA_EXPECT) == 0) {
> > -			rc = -EIO;
> > -			goto out_err;
> > -		}
> > -	}
> > +	rc = tpm_tis_write_bytes(priv, TPM_DATA_FIFO(priv->locality),
> > +			burstcnt, buf);
> Otherwise, this looks good but I don't understand why you assign 'len -
> 1' to 'brustcnt' and pass it to tpm_tis_write_bytes() instead of just
> passing 'len - 1'. I mean no relation to burst count, right?
Yeah, I can just send 'len - 1'. Will do this change.

Thanks & Regards,
ÂÂÂÂ - Nayna
> /Jarkko