linux-kernel - Re: [PATCH v4 3/4] tpm: reduce tpm polling delay in tpm_tis

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Message-ID: <20171018152447.b6scwbbmulrfzymw@linux.intel.com>
Date:   Wed, 18 Oct 2017 18:24:47 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Nayna Jain <nayna@...ux.vnet.ibm.com>
Cc:     linux-integrity@...r.kernel.org, zohar@...ux.vnet.ibm.com,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, peterhuewe@....de,
        tpmdd@...horst.net, jgunthorpe@...idianresearch.com,
        patrickc@...ibm.com
Subject: Re: [PATCH v4 3/4] tpm: reduce tpm polling delay in tpm_tis_core

On Tue, Oct 17, 2017 at 04:32:31PM -0400, Nayna Jain wrote:
> The existing wait_for_tpm_stat() polls for the chip status after
> 5msec sleep. As per TCG ddwg input, it is expected that tpm might
> return status in few usec. So, reducing the delay in polling to
> 1msec.
> Similarly, get_burstcount() function sleeps for 5msec before
> retrying for next query to burstcount in a loop. If it takes
> lesser time for TPM to return, this 5msec delay is longer than
> necessary.
> 
> After this change, performance on a TPM 1.2 with an 8 byte
> burstcount for 1000 extends improved from ~14sec to ~9sec.
> 
> Signed-off-by: Nayna Jain <nayna@...ux.vnet.ibm.com>

Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>

/Jarkko

> ---
>  drivers/char/tpm/tpm_tis_core.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index 993328ae988c..8b55fdaa67f2 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -31,6 +31,12 @@
>  #include "tpm.h"
>  #include "tpm_tis_core.h"
>  
> +/* This is a polling delay to check for status and burstcount.
> + * As per ddwg input, expectation is that status check and burstcount
> + * check should return within few usecs.
> + */
> +#define TPM_POLL_SLEEP	1  /* msec */
> +
>  static bool wait_for_tpm_stat_cond(struct tpm_chip *chip, u8 mask,
>  					bool check_cancel, bool *canceled)
>  {
> @@ -82,7 +88,7 @@ static int wait_for_tpm_stat(struct tpm_chip *chip, u8 mask,
>  		}
>  	} else {
>  		do {
> -			tpm_msleep(TPM_TIMEOUT);
> +			tpm_msleep(TPM_POLL_SLEEP);
>  			status = chip->ops->status(chip);
>  			if ((status & mask) == mask)
>  				return 0;
> @@ -224,7 +230,7 @@ static int get_burstcount(struct tpm_chip *chip)
>  		burstcnt = (value >> 8) & 0xFFFF;
>  		if (burstcnt)
>  			return burstcnt;
> -		tpm_msleep(TPM_TIMEOUT);
> +		tpm_msleep(TPM_POLL_SLEEP);
>  	} while (time_before(jiffies, stop));
>  	return -EBUSY;
>  }
> -- 
> 2.13.3
>