On Thu, Feb 13, 2014 at 10:42:01AM +0000, Wangyufei (James) wrote:
-----Original Message----- From: Martin Kletzander [mailto:mkletzan@redhat.com] Sent: Thursday, February 13, 2014 6:08 PM To: Wangyufei (James) Cc: libvir-list@redhat.com; Wangrui (K); Zhaoyanbin (A) Subject: Re: [libvirt] [PATCH] cpu: break out when a right cpuCandidate found
On Thu, Feb 13, 2014 at 07:44:20AM +0000, Wangyufei (James) wrote:
From 8123c5d64f940fa0fb0de32fc5e68035980b6b01 Mon Sep 17 00:00:00 2001 From: WangYufei <james.wangyufei@huawei.com> Date: Thu, 13 Feb 2014 07:17:11 +0000 Subject: [PATCH] cpu: break out when a right cpuCandidate found
In function x86Decode there's a code segment in while cycle like this: if (cpuModel == NULL || cpuModel->nfeatures > cpuCandidate->nfeatures) { virCPUDefFree(cpuModel); cpuModel = cpuCandidate; cpuData = candidate->data; } else { virCPUDefFree(cpuCandidate); } when it finds the right cpuCandidate, it doesn't break out the cycle, but continues run in it, and cpuModel will never get a new value, it's meaningless. It should break out when a right cpuCndidate found.
Inside this condition, the code doesn't always choose the perfect candidate. You don't consider a situation when the cycle continues and the next candidate model is the preferred one, thus satisfies previous condition, which looks like this:
if (preferred && STREQ(cpuCandidate->model, preferred)) { virCPUDefFree(cpuModel); cpuModel = cpuCandidate; cpuData = candidate->data; break; }
Where the "perfect" cpuModel is found, used and the condition breaks (appropriately this time). But I could also misunderstood the code.
Well, thank you for your reply. I have seen preferred, but there's no where to modify the value of preferred in the cycle. So the preferred is a fixed value. In this case, I can make it better to mdify the patch like this: --- a/src/cpu/cpu_x86.c +++ b/src/cpu/cpu_x86.c @@ -1558,6 +1558,7 @@ x86Decode(virCPUDefPtr cpu, virCPUDefFree(cpuModel); cpuModel = cpuCandidate; cpuData = candidate->data; + if (!preferred) + break; } else { virCPUDefFree(cpuCandidate); }
In my situation： virQEMUCapsInitCPU ->cpuDecode ->x86Decode if (!(data = cpuNodeData(arch)) || cpuDecode(cpu, data, NULL, 0, NULL) < 0) goto cleanup; preferred is always NULL. So we can do it better.
I think I'd like to see a test case which demonstrates the flawed behaviour and so proves the fix works. We already have a file tests/cputest.c in which to put such test cases. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|