On 07/08/14 10:21, Raghavendra K T wrote: > On 08/05/2014 08:14 PM, Christian Borntraeger wrote: >> We currently track the pid of the task that runs the VCPU in >> vcpu_load. Since we call vcpu_load for all kind of ioctls on a >> CPU, this causes hickups due to synchronize_rcu if one CPU is >> modified by another CPU or the main thread (e.g. initialization, >> reset). We track the pid only for the purpose of yielding, so >> let's update the pid only in the KVM_RUN ioctl. >> >> In addition, don't do a synchronize_rcu on startup (pid == 0). >> >> This speeds up guest boot time on s390 noticably for some configs, e.g. >> HZ=100, no full state tracking, 64 guest cpus 32 host cpus. >> >> Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> >> CC: Rik van Riel <riel@xxxxxxxxxx> >> CC: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx> >> CC: Michael Mueller <mimu@xxxxxxxxxxxxxxxxxx> >> --- > > Please feel free to add > Reviewed-by: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx> > > I could see very small improvement while testing 32 vcpu guest booting > on x86 (16 pcpu host +ht). > > I was just wondering whether somebody implementing vcpu hot plug would > have to bother about this change, but could not see any. What do you > think? The yield code can handle pid == 0, so the new CPU wont be a yield candidate until run for the first time. So I guess this is ok. Paolo, are you willing to apply to kvm/queue? Christian -- 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
