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

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Martin Cerveny [mailto:martin@xxxxxxxxx]
> Sent: 13 October 2016 03:17
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> Subject: RE: [win-pv-devel] Very slow shared memory (gnttab)
> 
> 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.
> 

Glad that works, but it does illustrate that using the PCI hole is problematic. 
This may be biting us when handling events, since the event fifos are mapped 
there too. I'll have a look into it.

Thanks fo the heads-up.

  Paul

> 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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