Re: [win-pv-devel] Very slow shared memory (gnttab)

[Martin Cerveny <martin@xxxxxxxxx>]

Hello.

Overnigth update - I reverted allocation:
- Windows exported (IOCTL_XENIFACE_GNTTAB_PERMIT_FOREIGN_ACCESS)
- dom0 imported (xc_gnttab_map_domain_grant_refs())
... and memcpy() working in both direction in Dom0/DomU at maximum speed ~ > 
8GB/s !

Ok, I will use this approach.

M.C>


On Thu, 13 Oct 2016, Paul Durrant wrote:

> > -----Original Message-----
> > From: win-pv-devel [mailto:win-pv-devel-bounces@xxxxxxxxxxxxxxxxxxxx] On
> > Behalf Of Martin Cerveny
> > Sent: 11 October 2016 14:50
> > To: win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> > Subject: [win-pv-devel] Very slow shared memory (gnttab)
> >
> > Hello.
> >
> > I am facing very slow sharable memory (memcpy()) from Windows Guest
> > (linux guests are Ok).
> > - write to sharable memory ~ 2MB/s (NOT GB)
> > - read from sharable memory ~ 4MB/s (NOT GB)
> > - r/w from/to local memory ~ > 8GB/s
> My guess would be that, because grants are mapped in the 'hole' which is the 
> platform PCI device's BAR space, that the memory accesses are uncached, and so 
> are very very slow.
>
>  Paul
>
> > - Dom0 shared 2048 refs (8MB RAM) (xc_gntshr_share_pages())
> > - window7 x64 imported
> > (IOCTL_XENIFACE_GNTTAB_MAP_FOREIGN_PAGES)
> > - memcpy() to copy ~ 2MB data
> >
> > - XenIface 8.2.0.51 (12.8.2016)
> > - XenBus 8.2.0.125 (21.9.2016)
> > - Windows 7SP1 + all patches
> > - VS2013
> > - Xen4.5.3, Xen4.6.1, Xen4.7.0
> > - Dom0 kernel XenServer kernel-3.10.41-332.380424 or kernel-3.10.96-
> > 484.383030
> >
> > What is wrong ?
> > Are there any tunables ?
> >
> > Thanks for answer, Martin Cerveny
> >
> > _______________________________________________
> > win-pv-devel mailing list
> > win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> > https://lists.xenproject.org/cgi-bin/mailman/listinfo/win-pv-devel
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