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Re: grep speed on Opteron vs P4



>T. Horsnell wrote:
>> I'm seeing huge discrepancies in grep speed between
>> my Opteron box and P4 boxes.
>> 
>> The Opteron box:
>> ----------------
>> 
>> Dual Opteron 248, 2.2GHz, 1MB cache, 8GB memory, RHEL4
>> ls1_tsh> uname -a
>> Linux ls1.lmb.internal 2.6.9-22.0.1.ELsmp #1 SMP Tue Oct 18 18:39:02 EDT 2005 x86_64 x86_64 x86_64 GNU/Linux
>> ls1_tsh> grep -V
>> grep (GNU grep) 2.5.1
>> 
>> 
>> grepping thro an 800 MB file:
>> 
>> ls1_tsh> time grep rubbishrubbish /tshgrp0/tsh/junkjunk
>> 41.618u 1.263s 0:43.30 99.0%    0+0k 0+0io 0pf+0w
>> ls1_tsh> time grep rubbishrubbish /tshgrp0/tsh/junkjunk
>> 41.675u 1.477s 0:43.54 99.0%    0+0k 0+0io 0pf+0w
>> 
>> ls1_tsh> ls -l  /tshgrp0/tsh/junkjunk
>> -rw-r--r--  1 tsh tsh 869243540 Sep  5 13:13 /tshgrp0/tsh/junkjunk
>> 
>> I'm certain the file is all stored in cache during this, and
>> that no disk accesses are taking place, because:
>> 1. 'top' shows grep at 99.9% cpu
>> 2. iostat on the disk in question shows zero activity.
>> 
>> The P4 box:
>> -----------
>> 
>> Monocore P4, 3.4GHz, 1MB cache, 2GB memory, FC3.
>> fm22_tsh> uname -a
>> Linux fm22.lmb.internal 2.6.11-1.35_FC3 #1 Mon Jun 13 00:52:08 EDT 2005 i686 i686 i386 GNU/Linux
>> fm22_tsh> grep -V
>> grep (GNU grep) 2.5.1
>> 
>> 
>> fm22_tsh> time grep rubbishrubbish /scr0/tsh/junkjunk
>> 0.272u 0.318s 0:00.59 98.3%     0+0k 0+0io 0pf+0w
>> fm22_tsh> time grep rubbishrubbish /scr0/tsh/junkjunk
>> 0.311u 0.281s 0:00.59 100.0%    0+0k 0+0io 0pf+0w
>> 
>> fm22_tsh> ls -l /scr0/tsh/junkjunk
>> -rw-r--r--  1 tsh users 869243540 Sep  5 14:29 /scr0/tsh/junkjunk
>> 
>> 
>> This is indicating that grep on the Opteron is *forty* times
>> slower than on the P4. Any ideas why this might be?
>> 64-bit nasties in grep? Has anyone else seen this?
>> 
>> Cheers,
>> Terry
>> 
>
>I find it hard to believe that any proessor could really grep an 800MB file in 
>1/4 of a second. I think your P4 system is lying to you.
>
>For example, grepping a 600MB RHEL CD iso I get the following figures:
>
>2.8GHz Pentium 4:
>real    0m20.531s
>user    0m17.138s
>sys     0m0.934s
>
>2.6GHz Opteron 852:
>real    0m9.858s
>user    0m9.415s
>sys     0m0.412s
>
>2.66GHz Xeon:
>real    0m18.545s
>user    0m17.559s
>sys     0m0.970s
>
>Are you sure that the P4 system is really looking at the same file, and is 
>successfully grepping the entire contents? It doesn't look like it is to me.

Yes, quite sure. The P4 box has 2GB mem and the whole file fits
into the buffer cache. So after an initial slow grep to get the
file into memory, the rest are that fast.

I've up2date'd the grep utility on the Opteron box, and it now does the
grep in 0.9 secs! (again, this is an 8GB mem machine, so the whole file
will fit into buffer cache).

Cheers,
Terry

>
>-- 
>Nigel Wade, System Administrator, Space Plasma Physics Group,
>             University of Leicester, Leicester, LE1 7RH, UK
>E-mail :    nmw ion le ac uk
>Phone :     +44 (0)116 2523548, Fax : +44 (0)116 2523555
>
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>fedora-list mailing list
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