Re: [PATCH v2 1/4] tpm: ignore burstcount to improve tpm_tis send() performance.

[Jarkko Sakkinen]

On Fri, Sep 15, 2017 at 05:59:21PM +0530, Nayna Jain wrote:
> 
> 
> On 09/14/2017 04:40 AM, Jarkko Sakkinen wrote:
> > On Wed, Sep 13, 2017 at 11:39:03AM -0700, Peter Huewe wrote:
> > > 
> > > Am 12. September 2017 17:45:08 GMT-07:00 schrieb Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>:
> > > > On Wed, Sep 06, 2017 at 08:56:36AM -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 adds an optimization to check for burstcount only once.
> > > > > And if it 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 41 msec to 14 msec.
> > > > > 
> > > > > This functionality is enabled only by passing module
> > > > > parameter ignore_burst_count=1. By default, this parameter
> > > > > is disabled.
> > > > > 
> > > > > 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>
> > > > > ---
> > > > >   Documentation/admin-guide/kernel-parameters.txt |  8 ++++++++
> > > > >   drivers/char/tpm/tpm_tis_core.c                 | 24
> > > > +++++++++++++++++++++---
> > > > >   2 files changed, 29 insertions(+), 3 deletions(-)
> > > > > 
> > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt
> > > > b/Documentation/admin-guide/kernel-parameters.txt
> > > > > index 4e303be83df6..3c59bb91e1ee 100644
> > > > > --- a/Documentation/admin-guide/kernel-parameters.txt
> > > > > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > > > > @@ -1465,6 +1465,14 @@
> > > > >   			mode generally follows that for the NaN encoding,
> > > > >   			except where unsupported by hardware.
> > > > > +	ignore_burst_count [TPM_TIS_CORE]
> > > > > +			tpm_tis_core driver queries for the burstcount before
> > > > > +			every send call in a loop. However, it causes delay to
> > > > > +			the send command for TPMs with low burstcount value.
> > > > > +			Setting this value to 1, will make driver to query for
> > > > > +			burstcount only once in the loop to improve the
> > > > > +			performance. By default, its value is set to 0.
> > > > > +
> > > > >   	ignore_loglevel	[KNL]
> > > > >   			Ignore loglevel setting - this will print /all/
> > > > >   			kernel messages to the console. Useful for debugging.
> > > > > diff --git a/drivers/char/tpm/tpm_tis_core.c
> > > > b/drivers/char/tpm/tpm_tis_core.c
> > > > > index 63bc6c3b949e..6b9bf4c4d434 100644
> > > > > --- a/drivers/char/tpm/tpm_tis_core.c
> > > > > +++ b/drivers/char/tpm/tpm_tis_core.c
> > > > > @@ -31,6 +31,11 @@
> > > > >   #include "tpm.h"
> > > > >   #include "tpm_tis_core.h"
> > > > > +static bool ignore_burst_count = false;
> > > > > +module_param(ignore_burst_count, bool, 0444);
> > > > > +MODULE_PARM_DESC(ignore_burst_count,
> > > > > +		"Ignore burstcount value while writing data");
> > > > > +
> > > > >   /* Before we attempt to access the TPM we must see that the valid
> > > > bit is set.
> > > > >    * The specification says that this bit is 0 at reset and remains 0
> > > > until the
> > > > >    * 'TPM has gone through its self test and initialization and has
> > > > established
> > > > > @@ -256,6 +261,7 @@ 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;
> > > > > +	int sendcnt;
> > > > >   	size_t count = 0;
> > > > >   	bool itpm = priv->flags & TPM_TIS_ITPM_WORKAROUND;
> > > > > @@ -271,19 +277,31 @@ static int tpm_tis_send_data(struct tpm_chip
> > > > *chip, u8 *buf, size_t len)
> > > > >   	}
> > > > >   	while (count < len - 1) {
> > > > > +
> > > > > +		/*
> > > > > +		 * Get the initial burstcount to ensure TPM is ready to
> > > > > +		 * accept data, even when waiting for burstcount is disabled.
> > > > > +		 */
> > > > >   		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);
> > > > > +
> > > > > +		if (ignore_burst_count)
> > > > > +			sendcnt = len - 1;
> > > > > +		else
> > > > > +			sendcnt = min_t(int, burstcnt, len - count - 1);
> > > > > +
> > > > >   		rc = tpm_tis_write_bytes(priv, TPM_DATA_FIFO(priv->locality),
> > > > > -					 burstcnt, buf + count);
> > > > > +					 sendcnt, buf + count);
> > > > >   		if (rc < 0)
> > > > >   			goto out_err;
> > > > > -		count += burstcnt;
> > > > > +		count += sendcnt;
> > > > > +		if (ignore_burst_count)
> > > > > +			continue;
> > > > >   		if (wait_for_tpm_stat(chip, TPM_STS_VALID, chip->timeout_c,
> > > > >   					&priv->int_queue, false) < 0) {
> > > > > -- 
> > > > > 2.13.3
> > > > > 
> > > > Makes sense to discuss whether to have the kernel command-line
> > > > parameter or not before applying this.
> > > > 
> > > > To fuel the discussion, alternative to this would be:
> > > > 
> > > > 1. Have this always on i.e. no command-line parameter.
> > > > 2. If someone yells, we add the command-line parameter later on.
> > > > 
> > > According to what I've read in the tcg ddwg group this patch should
> > > not cause problems on _sane_ tpms.
> > > 
> > > I'm not 100%convinced that all tpms are sane all the time, but I think
> > > we do not want yet another cmdline parameter.
> > > 
> > > So if we want to pull it in (and ddwg does not see an issue, so yes)
> > > it should be on by default, without a kernel parameter.
> > > 
> > > If there is a kernel parameter, then it should only be one called
> > > "failsafe" - which includes the force behavior and maybe the "broken"
> > > tpm path.
> > > 
> > > But I agree with Alex, every additonal code path reduces testing coverage.
> > > 
> > > 
> > > We would be happy to test a "default on" patch.
> > > 
> > > Peter
> > > 
> > > > /Jarkko
> > I'm starting to dilate to this direction.
> > 
> > It is hard to believe that any such TPM would be in active use anywhere
> > assuming that there exist a TPM where this causes issues. This combined
> > to the assumption that you would run the latest mainline on it makes it
> > a pretty insignificant scenario.
> 
> It sounds like we are getting in direction to have this change by default.
> Before removing the ignore_burst_count parameter, I will post a test version of this
> patch which enables ignore_burst_count by default, for testing purposes only.
> 
> Thanks Peter and Alex for testing.
> 
> Thanks & Regards,
>    - Nayna

I could apply it immediately after some testing to my next branch where
it gets pulled to linux-next. There's still a lot of time before next
pull request so many people would get exposed. If it cause problems,
we reconsider.

/Jarkko