linux-kernel - Re: [PATCH v3 3/5] tpm: reduce polling delay in tpm_tis wait_for_tpm

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Date:   Thu, 12 Oct 2017 14:17:26 +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 v3 3/5] tpm: reduce polling delay in tpm_tis
 wait_for_tpm_stat()

On Wed, Oct 04, 2017 at 06:29:22AM -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.
> 
> After this change, performance on a TPM 1.2 with an 8 byte
> burstcount for 1000 extends improved from ~14sec to ~10sec.
> 
> Signed-off-by: Nayna Jain <nayna@...ux.vnet.ibm.com>
> ---
>  drivers/char/tpm/tpm_tis_core.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index 8da425e1783f..224842e06105 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -31,6 +31,8 @@
>  #include "tpm.h"
>  #include "tpm_tis_core.h"
>  
> +#define TPM_POLL_SLEEP	1

Should have a comment above that explains the choice.

> +
>  static bool wait_for_tpm_stat_cond(struct tpm_chip *chip, u8 mask,
>  					bool check_cancel, bool *canceled)
>  {
> @@ -82,7 +84,7 @@ 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;
> -- 
> 2.13.3
> 

/Jarkko