Date: Sat, 27 Nov 2010 01:29:03 +0300 From: Lev Serebryakov <lev@FreeBSD.org> To: freebsd-geom@FreeBSD.org Subject: GEOM profiling - how to? Message-ID: <1299537757.20101127012903@serebryakov.spb.ru>
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Hello, Freebsd-geom. I'm doing some simple benchmarking of geom_raid5 in preparation of putting it into ports. And I notice strange results. It is array of 5 disks, stripsize=3D128k. All disks are SATA2 disks on ICH10R, AHCI driver (8.1-STABLE). Reading from device itself (dd with bs=3D512K) gives speed of one HDD exactly. gstat shows 100% load of RAID geom and 1/5 of this speed (and 18-22% load) on all disk GEOMs. Reading big file from FS (dd with bs=3D512k, FS block size = 32K, vfs.read_max=3D32) gives about twice speed and every disk GEOM is loaded 38-42%. CPU time is about 8% system, 0.5% interrupt, so CPU is not a bottle neck. Bigger block for "dd" doesn't wotk better. I want to know, why this configuration can not load disks up their top (and gives 4*HDD speed, about 320MB/s, speed). I even can not understand, why reeading from FS is beter than from raw device. Of course, I don't think you can me give answers for my questions. Really, I'm asking how could I peek into GEOM infrastructure to find bottle necks, understand why these two scenarios gives such different speed, etc. How could I profile I/O and GEOM? --=20 // Black Lion AKA Lev Serebryakov <lev@FreeBSD.org>
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