Re: [PATCH v2 0/2] read-cache: call verify_hdr() in a background thread

From: Jeff Hostetler <git@jeffhostetler.com>
Date: Mar 28, 2017, 15:30 UTC
Message-ID: <bf02e996-0b4b-f2ed-09b1-c99bb93c800f@jeffhostetler.com>
In-Reply-To: <20170327224505.ngp2gel3yvqcjrhw@sigill.intra.peff.net>

On 3/27/2017 6:45 PM, Jeff King wrote:

Show 33 quoted lines

> On Mon, Mar 27, 2017 at 09:09:37PM +0000, git@jeffhostetler.com wrote:
>
>> From: Jeff Hostetler <jeffhost@microsoft.com>
>>
>> Version 2 of this patch series simplifies this to just
>> turn off the hash verification.  Independent comments
>> from Linus and Peff suggested that we could just turn
>> this off and not worry about it.  So I've updated this
>> patch to do that.  I added a global variable to allow
>> the original code path to be used.  I also added a
>> t/helper command to demonstrate the differences.
>>
>> On the Linux repo, the effect is rather trivial:
>>
>>     $ ~/work/gfw/t/helper/test-skip-verify-index -c 3
>>     0.029884 0 [cache_nr 57994]
>>     0.031035 0 [cache_nr 57994]
>>     0.024308 0 [cache_nr 57994]
>>     0.028409 0 avg
>>     0.018359 1 [cache_nr 57994]
>>     0.017025 1 [cache_nr 57994]
>>     0.011087 1 [cache_nr 57994]
>>     0.015490 1 avg
>>
>> On my Windows source tree (450MB index), I'm seeing a
>> savings of 0.6 seconds -- read_index() went from 1.2 to 0.6
>> seconds.
>
> Very satisfying. I assume that was with OpenSSL as the SHA-1
> implementation (sha1dc would have been much slower on 450MB, I think).
>
> -Peff
>

Yes, this was with the OpenSSL SHA-1 code in a GfW build. I haven't played with the sha1dc code yet.

$ $/work/gh_gfw/t/helper/test-skip-verify-index.exe -c 5 1.276485 0 [cache_nr 3077831] 1.261164 0 [cache_nr 3077831] 1.256012 0 [cache_nr 3077831] 1.261411 0 [cache_nr 3077831] 1.266174 0 [cache_nr 3077831] 1.264249 0 avg 0.672057 1 [cache_nr 3077831] 0.666968 1 [cache_nr 3077831] 0.668725 1 [cache_nr 3077831] 0.675879 1 [cache_nr 3077831] 0.670213 1 [cache_nr 3077831] 0.670768 1 avg

Jeff