From: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
To: Nayna Jain <nayna@linux.vnet.ibm.com>
Cc: tpmdd-devel@lists.sourceforge.net, peterhuewe@gmx.de,
tpmdd@selhorst.net, jarkko.sakkinen@linux.intel.com,
linux-security-module@vger.kernel.org,
linux-kernel@vger.kernel.org,
linux-ima-devel@lists.sourceforge.net, patrickc@us.ibm.com
Subject: Re: [PATCH v2 1/4] tpm: ignore burstcount to improve tpm_tis send() performance.
Date: Wed, 6 Sep 2017 10:12:46 -0600 [thread overview]
Message-ID: <20170906161246.GA9747@obsidianresearch.com> (raw)
In-Reply-To: <20170906125643.5070-2-nayna@linux.vnet.ibm.com>
On Wed, Sep 06, 2017 at 08:56:36AM -0400, Nayna Jain wrote:
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 4e303be83df6..3c59bb91e1ee 100644
> +++ 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.
Really don't want to see a kernel command line parameter for this..
Please figure out a different approach or at least a better name..
> + /*
> + * 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);
The problem with this approach is that the TPM could totally block the CPU for
very long periods of time.
It seems very risky to enable..
Jason
next prev parent reply other threads:[~2017-09-06 16:12 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-06 12:56 [PATCH v2 0/4] additional TPM performance improvements Nayna Jain
2017-09-06 12:56 ` [PATCH v2 3/4] tpm: reduce tpm_msleep() time in get_burstcount() Nayna Jain
2017-09-13 1:00 ` Jarkko Sakkinen
2017-09-15 12:40 ` Nayna Jain
[not found] ` <20170906125643.5070-1-nayna-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
2017-09-06 12:56 ` [PATCH v2 1/4] tpm: ignore burstcount to improve tpm_tis send() performance Nayna Jain
2017-09-06 16:12 ` Jason Gunthorpe [this message]
2017-09-13 18:52 ` [tpmdd-devel] " Ken Goldman
[not found] ` <3c418974-a4c7-518e-b218-f6373c10209e-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
2017-09-13 19:01 ` Peter Huewe
2017-09-13 0:45 ` Jarkko Sakkinen
[not found] ` <20170912222010.ltm76m5vy2kupydi-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
2017-09-13 18:39 ` Peter Huewe
2017-09-13 23:10 ` Jarkko Sakkinen
2017-09-15 12:29 ` Nayna Jain
2017-09-15 15:19 ` Jarkko Sakkinen
2017-09-06 12:56 ` [PATCH v2 2/4] tpm: define __wait_for_tpm_stat to specify variable polling sleep time Nayna Jain
2017-09-13 0:58 ` Jarkko Sakkinen
2017-09-15 12:37 ` Nayna Jain
2017-09-15 15:20 ` Jarkko Sakkinen
2017-09-06 12:56 ` [PATCH v2 4/4] tpm: use tpm_msleep() value as max delay Nayna Jain
2017-09-13 0:47 ` Jarkko Sakkinen
2017-09-14 9:25 ` Nayna Jain
2017-09-14 12:28 ` Jarkko Sakkinen
2017-09-06 12:56 ` [PATCH 2/4] tpm: define __wait_for_tpm_stat to specify variable polling sleep time Nayna Jain
2017-09-06 12:58 ` Nayna
2017-09-06 12:56 ` [PATCH 1/4] tpm: ignore burstcount to improve tpm_tis send() performance Nayna Jain
[not found] ` <20170906125643.5070-6-nayna-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
2017-09-06 12:58 ` Nayna
2017-09-07 16:18 ` [PATCH v2 0/4] additional TPM performance improvements Jarkko Sakkinen
2017-09-11 15:20 ` [tpmdd-devel] " Alexander.Steffen
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