[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] RE: Writing to a ramdisk in a PV domain is SLLLOOOWWW?!?
It appears that ramswap is bad for HV domains also. On one run: real 11m38.017s user 0m6.696s sys 0m27.865s I tried on bare-metal Linux and there is a similar pattern but not nearly as bad: real 0m54.978s user 0m8.577s sys 0m3.094s Maybe there is some horrible TLB thrashing going on even on bare-metal that is made even worse by virtualization? > -----Original Message----- > From: Dan Magenheimer > Sent: Wednesday, May 05, 2010 12:14 PM > To: Xen-Devel (xen-devel@xxxxxxxxxxxxxxxxxxx) > Subject: Writing to a ramdisk in a PV domain is SLLLOOOWWW?!? > > Has anyone tried using a ramdisk in a PV domain? > > I'm trying it in an experiment to compare swapping to > a ramdisk against tmem (frontswap) performance > (suggested as a performance test on lkml). > > Writing to the ramdisk appears to be VERY VERY slow, > elapsed time in the guest is several times larger than > user+sys, and xentop shows the guest consuming vcpu > seconds at about the user+sys rate. Note that > this is when tmem is turned off and there is no > vhd swap disk configured. > > I'm suspecting that writing to ramdisk must be causing > some interesting/expensive PV pagetable behavior? > Or maybe somehow /dev/ram0 is getting routed through > qemu? Or ?? > > Thanks, > Dan > > P.S. Yes, I realize a ramdisk has no real value in > a guest... this is just a performance experiment. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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