[Xen-devel] slow xp hibernation revisited

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

I'm revisiting the problem where xp hangs on the first hibernation after
a boot. When the hibernate hangs for a while, strace -T -p shows around
600/second of:

mmap(NULL, 1048576, PROT_READ|PROT_WRITE, MAP_SHARED, 6, 0) =
0x7fb9cfa38000 <0.000036>
ioctl(6, IOCTL_PRIVCMD_MMAPBATCH_V2, 0x7fff2c8b0f20) = -1 EINVAL
(Invalid argument) <0.000027>
ioctl(6, IOCTL_PRIVCMD_MMAPBATCH, 0x7fff2c8b0f40) = 0 <0.002878>
munmap(0x7fb9cfa38000, 1048576) = 0 <0.000111>

Nothing like that is seen during normal execution, and the pause only
occurs on the first hibernate, never on subsequent hibernates (eg after
resume then hibernate again) until the DomU is rebooted. Working
backwards, those ioctl's appear to be called in libxc from
xc_map_foreign_xxx, but I'm getting a bit lost from there. Any
suggestions on how to track down what is causing this? Originally I
thought it might have been PoD memory causing the performance hit but
this DomU is fully populated aside from a few hundred kb.

Thanks

James

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