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

From: Nayna Jain
Date: Fri Sep 15 2017 - 08:41:09 EST

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;
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