Re: [Xen-devel] [PATCH for-4.5] tools/libxc: Avoid cacheflush toolstack hypercalls on x86

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2014-09-24 at 15:24 +0100, Andrew Cooper wrote:
> On 24/09/14 15:22, Ian Campbell wrote:
> > On Wed, 2014-09-24 at 14:47 +0100, Andrew Cooper wrote:
> >> XEN_DOMCTL_cacheflush hypercalls are (and will always be) -ENOSYS on x86, 
> >> but
> >> xc_domain_cacheflush() is called often during domain build and migrate for
> >> correct behaviour on ARM.
> >>
> >> Stub xc_domain_cacheflush() out on x86 to remove its pressure on the global
> >> domctl lock, and the hypercall overhead (which applies further pressure to 
> >> the
> >> already heavily-contended TLB flush lock).
> >>
> >> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> >> CC: Keir Fraser <keir@xxxxxxx>
> >> CC: Jan Beulich <JBeulich@xxxxxxxx>
> >> CC: Tim Deegan <tim@xxxxxxx>
> >> CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
> >> CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
> >> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> > Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> >
> > Although IMHO only the first paragraph of the comment is useful, the
> > rest belongs in the commit log (where it already mostly is already).
> 
> I am happy for that to be fixed while committing, or I could resubmit?

If you think it's just a case of nuking the other two paras then I'll do
it on commit, if you want to add some other words to the commit message
best to resubmit.

Ian.

> 
> ~Andrew
> 
> >
> >> ---
> >>  tools/libxc/xc_domain.c |   16 ++++++++++++++++
> >>  1 file changed, 16 insertions(+)
> >>
> >> diff --git a/tools/libxc/xc_domain.c b/tools/libxc/xc_domain.c
> >> index 1a6f90a..a68127f 100644
> >> --- a/tools/libxc/xc_domain.c
> >> +++ b/tools/libxc/xc_domain.c
> >> @@ -51,12 +51,28 @@ int xc_domain_create(xc_interface *xch,
> >>  int xc_domain_cacheflush(xc_interface *xch, uint32_t domid,
> >>                           xen_pfn_t start_pfn, xen_pfn_t nr_pfns)
> >>  {
> >> +#if defined (__i386__) || defined (__x86_64__)
> >> +    /*
> >> +     * The x86 architecture provides cache coherency guarantees which 
> >> prevent
> >> +     * the need for this hypercall.
> >> +     *
> >> +     * This call however is made frequently during domain build and 
> >> migrate
> >> +     * for the benefit of ARM, where cache flushes are needed.
> >> +     *
> >> +     * Stub it out here on x86 as domctls take the global domctl lock in 
> >> Xen
> >> +     * which is detrimental to concurrent toolstack operations on other
> >> +     * domains.
> >> +     */
> >> +    errno = ENOSYS;
> >> +    return -1;
> >> +#else
> >>      DECLARE_DOMCTL;
> >>      domctl.cmd = XEN_DOMCTL_cacheflush;
> >>      domctl.domain = (domid_t)domid;
> >>      domctl.u.cacheflush.start_pfn = start_pfn;
> >>      domctl.u.cacheflush.nr_pfns = nr_pfns;
> >>      return do_domctl(xch, &domctl);
> >> +#endif
> >>  }
> >>  
> >>  int xc_domain_pause(xc_interface *xch,
> >
> 



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel