Re: [libvirt] [PATCH] Fix performance & reliabilty of QMP probing

From: "Daniel P. Berrange" <berrange(a)redhat.com&gt;

This commit reverts the previous change, ensuring we do use the -daemonize flag to QEMU. Startup delay is cut from 7 seconds to 2 seconds on my machine, which is on a par with what it was prior to the capabilities rewrite. To deal with the fact that QEMU needs to be able to create the pidfile, we switch pidfile location fron runDir to libDir, which QEMU is guaranteed to be able to write to. Signed-off-by: Daniel P. Berrange <berrange(a)redhat.com&gt; --- src/qemu/qemu_capabilities.c | 50 ++++++++++++++++++++++++++++++-------------- src/qemu/qemu_capabilities.h | 3 +-- 2 files changed, 35 insertions(+), 18 deletions(-) @@ -916,11 +917,19 @@ virCapsPtr qemuCapsInit(qemuCapsCachePtr cache) * so just probe for them all - we gracefully fail * if a qemu-system-$ARCH binary can't be found */ - for (i = 0 ; i < VIR_ARCH_LAST ; i++) + unsigned long long a, b;

+ for (i = 0 ; i < VIR_ARCH_LAST ; i++) { + unsigned long long start, end; + if (virTimeMillisNow(&start) < 0) + goto error; if (qemuCapsInitGuest(caps, cache, virArchFromHost(), i) < 0) goto error; + if (virTimeMillisNow(&end) < 0) + goto error; + VIR_DEBUG("Probed %s in %llums", virArchToString(i), end-start);

+ } /* QEMU Requires an emulator in the XML */ virCapabilitiesSetEmulatorRequired(caps); @@ -2291,7 +2300,6 @@ qemuCapsInitQMPBasic(qemuCapsPtr caps) static int qemuCapsInitQMP(qemuCapsPtr caps, const char *libDir, - const char *runDir, uid_t runUid, gid_t runGid) { @@ -2324,8 +2332,11 @@ qemuCapsInitQMP(qemuCapsPtr caps, /* ".pidfile" suffix is used rather than ".pid" to avoid a possible clash * with a qemu domain called "capabilities" + * Normally we'd use runDir for pid files, but because we're using + * -daemonize we need QEMU to be allowed to create them, rather + * than libvirtd. So we're using libDir which QEMU can write to */ - if (virAsprintf(&pidfile, "%s/%s", runDir, "capabilities.pidfile") < 0) { + if (virAsprintf(&pidfile, "%s/%s", libDir, "capabilities.pidfile") < 0) {

+ /* + * We explicitly need to use -daemonize here, rather than + * virCommandDaemonize, because we need to synchronize + * with QEMU creating its monitor socket API. Using + * daemonize guarnatees control won't return to libvirt