On 04/11/2012 01:21 PM, Chegu Vinod wrote:
Hello, While running an AIM7 (workfile.high_systime) in a single 40-way (or a single 60-way KVM guest) I noticed pretty bad performance when the guest was booted with 3.3.1 kernel when compared to the same guest booted with 2.6.32-220 (RHEL6.2) kernel.
For the 40-way Guest-RunA (2.6.32-220 kernel) performed nearly 9x better than the Guest-RunB (3.3.1 kernel). In the case of 60-way guest run the older guest kernel was nearly 12x better !
Turned on function tracing and found that there appears to be more time being spent around the lock code in the 3.3.1 guest when compared to the 2.6.32-220 guest.
Looks like you may be running into the ticket spinlock code. During the early RHEL 6 days, Gleb came up with a patch to automatically disable ticket spinlocks when running inside a KVM guest. IIRC that patch got rejected upstream at the time, with upstream developers preferring to wait for a "better solution". If such a better solution is not on its way upstream now (two years later), maybe we should just merge Gleb's patch upstream for the time being? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
