[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Improving domU restore time
On Tue, May 25, 2010 at 12:50:40PM +0100, Keir Fraser wrote: > On 25/05/2010 11:35, "Rafal Wojtczuk" <rafal@xxxxxxxxxxxxxxxxxxxxxx> wrote: > > > a) Is it correct that when xc_restore runs, the target domain memory is > > already > > zeroed (because hypervisor scrubs free memory, before it is assigned to a > > new domain) > > There is no guarantee that the memory will be zeroed. Interesting. For my education, could you explain who is responsible for clearing memory of a newborn domain ? Xend ? Could you point me to the relevant code fragments ? It looks sensible to clear free memory in hypervisor context in its idle cycles; if non-temporal instructions (movnti) were used for this, it would not pollute caches, and it must be done anyway ? > > b) xen-3.4.3/xc_restore reads data from savefile in 4k portions - so, one > > read syscall per page. Make it read in larger chunks. It looks it is fixed > > in > > xen-4.0.0, is this correct ? > > It got changed a lot for Remus. I expect performance was on their mind. > Normally kernel's file readahead heuristic would get back most of the > performance of not reading in larger chunks. Yes, readahead would keep the disk request queue full, but I was just thinking of lowering the syscall overhead. 1e5 syscalls is a lot :) [user@qubes ~]$ dd if=/dev/zero of=/dev/null bs=4k count=102400 102400+0 records in 102400+0 records out 419430400 bytes (419 MB) copied, 0.307211 s, 1.4 GB/s [user@qubes ~]$ dd if=/dev/zero of=/dev/null bs=4M count=100 100+0 records in 100+0 records out 419430400 bytes (419 MB) copied, 0.25347 s, 1.7 GB/s RW _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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