>>How should we do read-ahead inside qemu? manually? This is managed by the linux kernel automaticaly
/sys/class/block/sda/queue/read_ahead_kb Also about ceph performance, another problem is that qemu is single threaded for block access. And ceph/librbd cpu usage is huge, so it's possible to be cpu bound on 1 core. I need to send a patch, but with virtio-scsi it's possible to do multi-queue, to scale on multi-cores, with "num_queue" param in virtio-scsi device. I'm not sure It's helping for the blocks jobs, but It's really helping the guest ios. Here some bench results on coming giant ceph release with differents tuning:(0.86) 8 cores (CPU E5-2603 v2 @ 1.80GHz): 15000 iops 4K read : auth_client: cephx rbd_cache: on (50% cpu) 25000 iops 4K read : auth_client: cephx rbd_cache: off (100% cpu - seem to have read lock with rbd_cache=true) 40000 iops 4K read : auth_client: none rbd_cache: off (100% cpu - cephx auth is really cpu intensive) And with 1 core, I can get only 7000 iops. (same inside the vm with virtio-blk) ----- Mail original ----- De: "Dietmar Maurer" <[email protected]> À: "Alexandre DERUMIER" <[email protected]> Cc: [email protected], "VELARTIS Philipp Dürhammer" <[email protected]>, "Dmitry Petuhov" <[email protected]> Envoyé: Dimanche 19 Octobre 2014 18:07:30 Objet: RE: [pve-devel] backup ceph high iops and slow > +RBD supports read-ahead/prefetching to optimize small, sequential reads. > +This should normally be handled by the guest OS in the case of a VM, How should we do read-ahead inside qemu? manually? _______________________________________________ pve-devel mailing list [email protected] http://pve.proxmox.com/cgi-bin/mailman/listinfo/pve-devel
