Messages in this thread |  | | Date | Wed, 31 Oct 2001 18:29:25 +0100 (CET) | From | Gérard Roudier <> | Subject | Re: The good, the bad & the ugly (or VM, block devices, and SCSI :-) |
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On Wed, 31 Oct 2001, Stephan von Krawczynski wrote:
> Hello all, > > this is a message especially for: > > Gerard Roudier <groudier@club-internet.fr>, symbios driver > Justin T. Gibbs, adaptec driver > Andrea and Rik, VM > Linus, the man with the big picture :-) > > Everything started with a note from a friend who tried some small all-in-one > box with a sym53c1010 onboard. He (an all-time adaptec user like me) told me > the small box feels like flying, compared to his at-home box (with adaptec). > This made me curious for trying myself. I bought a Tekram DC390 U3W (which is > in fact a relabeled U3D) with symbios chipset. I simply replaced the controller > in my box (compiled a kernel with both drivers of course) and gave it a try > with bonnie. It did not look impressing. Effectively adaptec A29160 and DC390 > had the same read and write speeds, only noticeable was that tekram performed > twice as many seeks as adaptec. This was reproducable in all bonnie-tests. Hm, > that should not make the big difference. Anyway I was too lazy to put the > adaptec back in and continued working (for several days). Today it hit me: > As Linus said something about testing pre6 I gave it a try and did the usual > nfs-copy, cd read test. I was pretty astonished to see the tekram perform very > well under heavy I/O load, here are the numbers: > > A29160: symbios: > > cd read without nfs-load: cd read without nfs-load > 2998,9 kB 3619,3 kB > 3168,2 kB 3611,1 kB > 2968,4 kB 3620,2 kB > > cd read with nfs load: cd read with nfs load > 1926,2 kB 3408,1 kB > 2123,4 kB 3395,2 kB > 2539,4 kB 3605,1 kB > 2631,9 kB 3605,8 kB > > The rest of the hardware involved is completely the same, only the controller > boards got exchanged. Another thing quite remarkable: during symbios tests the > network throughput derived from nfs load is _higher_ and looks more stable. > Whereas during adaptec the whole picture looks like having hiccup. More to say: > starting an application during the tests results in waiting a bit (some 10-20 > seconds) with tekram, but waiting pretty long (or even forever, "the ugly" ;-) > while using adaptec. This is particularly interesting for the vm guys since all > the scene is in high vm load with around 3-5 MB of free mem and a damn lot of > page cache. So if you try something around vm I can only urge you to perform > tests that do _no_ I/O at all, because you may be greatly bitten by your > controller (or its driver). > Another thing to mention: during the last cd-read tests with tekram setup I > already have been deeply impressed by the driver, so I decided to stress it > some more and start applications (like mozilla) in the background. And in the > end I was even more impressed, because it turned out (you can see in the last > two figures), that it got even _faster_. Obviously I cannot explain why. > If anybody wants me to test anything, feel free to ask. > > My personal opinion: Justin has work to do.
Agreed here. Justin should write a clean SCSI access method for Linux for free as he did for FreeBSD. :-)
Just considering the CD read thoughtput differences, we cannot get any useful information that applies to software driver differences from your report. Given the very low throughput it involves (about 3 MB/s) compared to the capabilities of the controllers (160 MB/s), the results should be explainable by something related to difference in configuration or to some hardware or kernel weirdness. I cannot believe a single second that the difference is due to the software drivers.
Thanks, anyway, for your report.
Regards, Gérard.
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