On 03/16/2017 06:29 PM, Alberto Garcia wrote: > On Thu 16 Mar 2017 04:08:50 PM CET, Daniel P. Berrange wrote: >>> OK. How could I change L2 cache size for QCOW2 image? >>> >>> For 1 Tb disk, fragmented in guest, the performance loss is >>> around 10 times. 10 TIMES. 1000%. The customer could not >>> wait until proper fix in the next QEMU release especially >>> if we are able to provide the kludge specifically for him. >> We can explicitly allow L2 cache size set in the XML but that >> is a pretty poor solution to the problem IMHO, as the mgmt >> application has no apriori knowledge of whether a particular >> cache size is going to be right for a particular QCow2 image. >> >> For a sustainable solution, IMHO this really needs to be fixed >> in QEMU so it has either a more appropriate default, or if a >> single default is not possible, have QEMU auto-tune its cache >> size dynamically to suit the characteristics of the qcow2 image. > Related bug report (and discussion): > > https://bugzilla.redhat.com/show_bug.cgi?id=1377735 > > Berto Very useful! Thank you. I have different approach for the case. Though I do not have numbers, but with a big data block the price for cache miss is too big. I'll try to come back with this later on. Den -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
