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    DateWed, 21 Mar 2007 08:40:14 +0100
    FromJens Axboe <>
    SubjectRe: AIO, FIO and Threads ...
    On Tue, Mar 20 2007, Davide Libenzi wrote:
    > 
    > I was looking at Jens FIO stuff, and I decided to cook a quick patch for 
    > FIO to support GUASI (Generic Userspace Asyncronous Syscall Interface):
    > 
    > http://www.xmailserver.org/guasi-lib.html
    > 
    > I then ran a few tests on my Dual Opteron 252 with SATA drives (sata_nv) 
    > and 8GB of RAM.
    > Mind that I'm not FIO expert, like at all, but I got some interesting 
    > results when comparing GUASI with libaio at 8/1000/10000 depths.
    > If I read those result correctly (Jens may help), GUASI output is more 
    > then double the libaio one.
    > Lots of context switches, yes. But the throughput looks like 2+ times.
    > Can someone try to repeat the measures and/or spot the error?
    > Or tell me which other tests to run?
    > This is kinda a suprise for me ...
    
    I don't know guasi at all, but libaio requires O_DIRECT to be async. I'm
    sure you know this, but you may not know that fio default to buffered IO
    so you have to tell it to use O_DIRECT :-)
    
    So try adding a --direct=1 (or --buffered=0, same thing) as an extra
    option when comparing depths > 1.
    I'll add your guasi engine, but disable it. Unfortunately fio still
    doesn't have a nifty configure setup, so these things are still
    manual...
    
    -- 
    Jens Axboe
    
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