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Subject: Re: [PATCH v2 1/2] tpm: reduce poll sleep time in tpm_transmit()
From:   Mimi Zohar <zohar@linux.vnet.ibm.com>
To:     Nayna Jain <nayna@linux.vnet.ibm.com>,
        linux-integrity@vger.kernel.org
Cc:     linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org, peterhuewe@gmx.de,
        jarkko.sakkinen@linux.intel.com, tpmdd@selhorst.net,
        jgunthorpe@obsidianresearch.com, patrickc@us.ibm.com
Date:   Wed, 18 Apr 2018 11:01:48 -0400
In-Reply-To: <20180417131246.434-2-nayna@linux.vnet.ibm.com>
References: <20180417131246.434-1-nayna@linux.vnet.ibm.com>
         <20180417131246.434-2-nayna@linux.vnet.ibm.com>
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On Tue, 2018-04-17 at 09:12 -0400, Nayna Jain wrote:
> The TPM polling code in tpm_transmit sleeps in each loop iteration for
> 5 msecs. However, the TPM might return earlier, and thus waiting for
> 5 msecs adds an unnecessary delay. This patch reduces the polling sleep
> time in tpm_transmit() from 5 msecs to 1 msecs.
> 
> Additionally, this patch renames TPM_POLL_SLEEP and moves it to tpm.h as
> an enum value.
> 
> After this change, performance on a TPM 1.2 with an 8 byte burstcount
> for 1000 extends improved from ~14 sec to ~10.7 sec.
> 
> Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com>

Reviewed-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

> ---
>  drivers/char/tpm/tpm-interface.c |  2 +-
>  drivers/char/tpm/tpm.h           |  3 ++-
>  drivers/char/tpm/tpm_tis_core.c  | 10 ++--------
>  3 files changed, 5 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> index 9e80a953d693..a676d8ad5992 100644
> --- a/drivers/char/tpm/tpm-interface.c
> +++ b/drivers/char/tpm/tpm-interface.c
> @@ -470,7 +470,7 @@ ssize_t tpm_transmit(struct tpm_chip *chip, struct tpm_space *space,
>  			goto out;
>  		}
> 
> -		tpm_msleep(TPM_TIMEOUT);
> +		tpm_msleep(TPM_TIMEOUT_POLL);
>  		rmb();
>  	} while (time_before(jiffies, stop));
> 
> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
> index f895fba4e20d..7e797377e1eb 100644
> --- a/drivers/char/tpm/tpm.h
> +++ b/drivers/char/tpm/tpm.h
> @@ -53,7 +53,8 @@ enum tpm_const {
>  enum tpm_timeout {
>  	TPM_TIMEOUT = 5,	/* msecs */
>  	TPM_TIMEOUT_RETRY = 100, /* msecs */
> -	TPM_TIMEOUT_RANGE_US = 300	/* usecs */
> +	TPM_TIMEOUT_RANGE_US = 300,	/* usecs */
> +	TPM_TIMEOUT_POLL = 1	/* msecs */
>  };
> 
>  /* TPM addresses */
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index da074e3db19b..021e6b68f2db 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -31,12 +31,6 @@
>  #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 void tpm_tis_clkrun_enable(struct tpm_chip *chip, bool value);
> 
>  static bool wait_for_tpm_stat_cond(struct tpm_chip *chip, u8 mask,
> @@ -90,7 +84,7 @@ static int wait_for_tpm_stat(struct tpm_chip *chip, u8 mask,
>  		}
>  	} else {
>  		do {
> -			tpm_msleep(TPM_POLL_SLEEP);
> +			tpm_msleep(TPM_TIMEOUT_POLL);
>  			status = chip->ops->status(chip);
>  			if ((status & mask) == mask)
>  				return 0;
> @@ -232,7 +226,7 @@ static int get_burstcount(struct tpm_chip *chip)
>  		burstcnt = (value >> 8) & 0xFFFF;
>  		if (burstcnt)
>  			return burstcnt;
> -		tpm_msleep(TPM_POLL_SLEEP);
> +		tpm_msleep(TPM_TIMEOUT_POLL);
>  	} while (time_before(jiffies, stop));
>  	return -EBUSY;
>  }