linux-kernel - Re: [PATCH v2 1/2] tpm: reduce poll sleep time in tpm

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Message-ID: <20180424162752.GC5119@linux.intel.com>
Date:   Tue, 24 Apr 2018 19:27:52 +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 v2 1/2] tpm: reduce poll sleep time in tpm_transmit()

On Tue, Apr 17, 2018 at 09:12:45AM -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.

I'm not sure what TPM returning earlier has to do with this. TPM probably
never returns exactly in the spec defined timeout/duration. I just don't
understand reasoning in this paragraph.

> 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.

You cannot give absolute numbers without a context (platform, software).

> Signed-off-by: Nayna Jain <nayna@...ux.vnet.ibm.com>

/Jarkko