On Wed, Dec 13, 2006 at 04:37:42PM +0000, Dieter wrote: > > > Is Giant the only mutex/lock that could be a bottleneck across disks? > > > > The only one I can think of that is generic. One would have to do > > more extensive profiling and diagnosis to try and figure out what is > > wrong with your system. > > Suggestions of what to look at would be welcome.
Mutex profiling would show if there is a mutex somehow getting in the way of your I/O (e.g. if Giant is somehow being forced). I dont think it would show anything though. You can try to study interrupt issues (e.g. look for an interrupt storm during I/O) with vmstat -i. Other than that you'd probably have to get your hands dirtier in the code. > > The only explanation that seems to fit is that it's something to do > > with your particular hardware (i.e. driver issue), since it's > > certainly not a problem on general configurations. > > > > I know that many people have bad things to say about nforce chipsets, > > although I dont know if your particular problem has been reported > > before. > > Could APIC have anything to do with this? It is currently turned off in > firmware. Problems with interrupt delivery could certainly be relevant. > Today I experimented with vfs.hirunningspace. If I crank it up, I get > better total write speed with multiple drives doing dd from /dev/zero > to files on disks. But it doesn't help my real applications, and > in fact appears to hurt them. Yes, I don't expect there are any viable high-level workarounds for this issue at a lower layer. Kris
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