tpmdd-devel.lists.sourceforge.net archive mirror
 help / color / mirror / Atom feed
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

  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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20170906161246.GA9747@obsidianresearch.com \
    --to=jgunthorpe@obsidianresearch.com \
    --cc=jarkko.sakkinen@linux.intel.com \
    --cc=linux-ima-devel@lists.sourceforge.net \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-security-module@vger.kernel.org \
    --cc=nayna@linux.vnet.ibm.com \
    --cc=patrickc@us.ibm.com \
    --cc=peterhuewe@gmx.de \
    --cc=tpmdd-devel@lists.sourceforge.net \
    --cc=tpmdd@selhorst.net \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).