From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH for-4.5] tools/libxc: Avoid cacheflush toolstack hypercalls on x86 Date: Wed, 24 Sep 2014 15:24:41 +0100 Message-ID: <5422D429.8000903@citrix.com> References: <1411566472-11308-1-git-send-email-andrew.cooper3@citrix.com> <1411568558.28127.42.camel@kazak.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1411568558.28127.42.camel@kazak.uk.xensource.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell Cc: Wei Liu , Ian Jackson , Tim Deegan , Xen-devel , Jan Beulich , Keir Fraser List-Id: xen-devel@lists.xenproject.org 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 >> CC: Keir Fraser >> CC: Jan Beulich >> CC: Tim Deegan >> CC: Ian Campbell >> CC: Ian Jackson >> CC: Wei Liu > Acked-by: Ian Campbell > > 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? ~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, >