On Mon, 2014-08-11 at 13:52 -0700, Nicholas A. Bellinger wrote: > (Responding again without gmail, as the last email hit a failure when > responding to the lists..) > > On Mon, 2014-08-11 at 16:17 -0400, Alexander Gordeev wrote: > > On Fri, Jul 18, 2014 at 12:20:56PM +0200, Alexander Gordeev wrote: > > > The performance test is not decent, though. I used "fio" random > > > read against a "null_blk" device sitting on top of "percpu_tags", > > > which is not exactly how "percpu_ida" is used. This is another > > > reason I am posting - an advice on how to properly test is very > > > appreciated. > > > > Hi Nicholas et al, > > > > I expect the best possible performance test for percpu_ida/percpu_tags > > would be to stress drivers/vhost/scsi.c vhost_scsi_get_tag() function. > > > > I tried to make such test by attaching ramdisk to a virtual machine > > (similar to https://lkml.org/lkml/2012/8/10/347) but ultimately failed > > to configure the necessary environment - the stock qemu does not have > > -vhost-scsi parameter. > > > > Could you please advice how to make this configuration exposed to guests? > > > > o- / ..................................................................... > > [...] > > o- backstores .......................................................... > > [...] > > | o- block .............................................. [Storage > > Objects: 0] > > | o- fileio ............................................. [Storage > > Objects: 0] > > | o- pscsi .............................................. [Storage > > Objects: 0] > > | o- ramdisk ............................................ [Storage > > Objects: 1] > > | o- rda .............................................. [(1.0GiB) > > activated] > > o- iscsi ........................................................ > > [Targets: 0] > > o- loopback ..................................................... > > [Targets: 0] > > o- vhost ........................................................ > > [Targets: 1] > > o- naa.5001405b171ee405 .......................................... > > [TPGs: 1] > > o- tpg1 .............................. [naa.5001405983a5b1a4, > > no-gen-acls] > > o- acls ...................................................... > > [ACLs: 0] > > o- luns ...................................................... > > [LUNs: 1] > > o- lun0 ................................................ > > [ramdisk/rda] > > > > So qemu expects '-device vhost-scsi-pci' with the following syntax: > > -device > vhost-scsi-pci,wwpn=naa.5001405b171ee405,num_queues=1,cmd_per_lun=64 > > For best results I'd recommend setting the IRQ affinity for each of the > virtio*_request MSI-X vectors to a dedicated vCPU in KVM guest. > > Also, I've been using the scsi-mq prototype for small block I/O > performance testing in order to push vhost-scsi and avoid the legacy > scsi_request_fn() bottleneck(s) with virtio-scsi, and now that hch's > scsi-mq work (CC'ed) has been merged upstream in v3.17-rc0, it would be > a good time for a scsi-mq + virtio-scsi + vhost-scsi performance > checkpoint. ;) >
Oh yeah, for performance testing you'll want to use the rd_nullio=1 flag when creating RAMDISK backends, to avoid the normal fast-path memcpys between ramdisk + per I/O descriptor memory. --nab -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
