From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: [PATCH v2 for-4.5] tools/libxc: Avoid cacheflush toolstack hypercalls on x86 Date: Wed, 24 Sep 2014 17:28:15 +0100 Message-ID: <1411576095-16790-1-git-send-email-andrew.cooper3@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Xen-devel Cc: Keir Fraser , Ian Campbell , Andrew Cooper , Ian Jackson , Tim Deegan , Jan Beulich , Wei Liu List-Id: xen-devel@lists.xenproject.org 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 --- v2: * Reduce wording in the patch, as it not really needed in the code, and is covered in the commit message --- tools/libxc/xc_domain.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/tools/libxc/xc_domain.c b/tools/libxc/xc_domain.c index 1a6f90a..6e0e355 100644 --- a/tools/libxc/xc_domain.c +++ b/tools/libxc/xc_domain.c @@ -51,12 +51,22 @@ 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. Avoid the overhead of making a hypercall + * just for Xen to return -ENOSYS. + */ + 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, -- 1.7.10.4