Re: AMD64 Machine hardlocks when using memset

[Arjan van de Ven]

On Wed, 2005-04-06 at 12:59 +0200, Philip Lawatsch wrote:
> Robert Hancock wrote:
> > Alan Cox wrote:
> > 
> >> On Sad, 2005-04-02 at 05:50, Robert Hancock wrote:
> >>
> >>> I'm wondering if one does a ton of these cache-bypassing stores
> >>> whether something gets hosed because of that. Not sure what that
> >>> could be though. I don't imagine the chipset is involved with any of
> >>> that on the Athlon 64 - either the CPU or RAM seems the most likely
> >>> suspect to me
> >>
> >>
> >>
> >> The glibc version is essentially the "perfect" copy function for the
> >> CPU. If you have any bus/memory problems or chipset bugs it will bite
> >> you.
> > 
> > 
> > Anyone have any suggestions on how to track this further? It seems
> > fairly clear what circumstances are causing it, but as for figuring out
> > what's at fault..
> 
> Digging through my glibc's source if found that if you memset arrays
> <120000 bytes it will use good old mov instructions to do the job. In
> case of arrays larger than 120000 bytes it will use movnti instructions
> to do the job.
> 
> Thus I refined my test code to use mov for memset regardless of the size
> (simply abused glibcs code a little bit)
> 
> -> No crash!
> 
> Then, changing the all the mov to movnti and my machine frags again :(
> 
> It seems that mov'ing does not kill my machine while simply using movnti
> does.

movnti also gets a higher bandwidth so that doesn't rule out too much..



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