Messages in this thread | | | Date | Fri, 21 Jun 2002 09:03:33 +0200 | From | Helge Hafting <> | Subject | Re: [Ext2-devel] Re: Shrinking ext3 directories |
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Daniel Phillips wrote:
> I ran a bakeoff between your new half-md4 and dx_hack_hash on Ext2. As > predicted, half-md4 does produce very even bucket distributions. For 200,000 > creates: > > half-md4: 2872 avg bytes filled per 4k block (70%) > dx_hack_hash: 2853 avg bytes filled per 4k block (69%) > > but guess which was faster overall? > > half-md4: user 0.43 system 6.88 real 0:07.33 CPU 99% > dx_hack_hash: user 0.43 system 6.40 real 0:06.82 CPU 100% > > This is quite reproducible: dx_hack_hash is always faster by about 6%. This > must be due entirely to the difference in hashing cost, since half-md4 > produces measurably better distributions. Now what do we do?
No surprise that the worse distribution is faster - you get less io when fewer blocks are used. Which means a bad distribution beats a good one _until_ blocks start to really fill up and collide. 2.8K per 4K block is only 70% full. I guess the better hash wins if you force a higher fill rate?
Helge Hafting - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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