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SubjectRe: [PATCH v2 1/4] tpm: ignore burstcount to improve tpm_tis send() performance.
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@linux.vnet.ibm.com> in
> conjunction with the TPM Device Driver work group.
> Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com>
> Acked-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
> ---
> 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.

/Jarkko

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