Re: Long clone time after "done."

From: Uri Moszkowicz <uri@4refs.com>
Date: Nov 26, 2012, 18:06 UTC
Message-ID: <CAMJd5AQAYt7tBVPrC6KVSa7nEfoWTAHnDZKUPS7QBCFxR5THkw@mail.gmail.com>
In-Reply-To: <CAMJd5AQOH=uu1c3enr5fES+Bw4FHZuP++J7-aCM2B+f_G3YMtg@mail.gmail.com>

Hi guys, Any further interest on this scalability problem or should I move on?

Thanks, Uri

On Thu, Nov 8, 2012 at 5:35 PM, Uri Moszkowicz <uri@4refs.com> wrote:

Show 50 quoted lines

> I tried on the local disk as well and it didn't help. I managed to
> find a SUSE11 machine and tried it there but no luck so I think we can
> eliminate NFS and OS as significant factors now.
>
> I ran with perf and here's the report:
>
> ESC[31m    69.07%ESC[m              git  /lib64/libc-2.11.1.so
>                                          [.] memcpy
> ESC[31m    12.33%ESC[m              git
> <prefix>/git-1.8.0.rc2.suse11/bin/git                           [.]
> blk_SHA1_Block
> ESC[31m     5.11%ESC[m              git
> <prefix>/zlib/local/lib/libz.so.1.2.5                           [.]
> inflate_fast
> ESC[32m     2.61%ESC[m              git
> <prefix>/zlib/local/lib/libz.so.1.2.5                           [.]
> adler32
> ESC[32m     1.98%ESC[m              git  /lib64/libc-2.11.1.so
>                                          [.] _int_malloc
> ESC[32m     0.86%ESC[m              git  [kernel]
>                                          [k] clear_page_c
>
> Does this help? Machine has 396GB of RAM if it matters.
>
> On Thu, Nov 8, 2012 at 4:33 PM, Jeff King <peff@peff.net> wrote:
>> On Thu, Nov 08, 2012 at 04:16:59PM -0600, Uri Moszkowicz wrote:
>>
>>> I ran "git cat-file commit some-tag" for every tag. They seem to be
>>> roughly uniformly distributed between 0s and 2s and about 2/3 of the
>>> time seems to be system. My disk is mounted over NFS so I tried on the
>>> local disk and it didn't make a difference.
>>>
>>> I have only one 1.97GB pack. I ran "git gc --aggressive" before.
>>
>> Ah. NFS. That is almost certainly the source of the problem. Git will
>> aggressively mmap. I would not be surprised to find that RHEL4's NFS
>> implementation is not particularly fast at mmap-ing 2G files, and is
>> spending a bunch of time in the kernel servicing the requests.
>>
>> Aside from upgrading your OS or getting off of NFS, I don't have a lot
>> of advice.  The performance characteristics you are seeing are so
>> grossly off of what is normal that using git is probably going to be
>> painful. Your 2s cat-files should be more like .002s. I don't think
>> there's anything for git to fix here.
>>
>> You could try building with NO_MMAP, which will emulate it with pread.
>> That might fare better under your NFS implementation. Or it might be
>> just as bad.
>>
>> -Peff