Damn, I have redone test with a 3.6 guest kernel, and now it's work fine.
So writeback in guest is the default if nocache= is defined.
Don't know if on the host side, cache is enable (none or writeback)
But if I understand the default cache on qemu 1.1 was writethrough in guest.
(so directsync or writethrough on host).
And not none, as it's in pve-manager currently.
I'll do same test with qemu 1.1 to be sure.
qemu 1.2
ide
---
no cache defined : hdparm -W /dev/sda : on
cache=none : hdparm -W /dev/sda : on
cache=writeback : hdparm -W /dev/sda : on
cache=writethrough : hdparm -W /dev/sda : off
cache=directsync : hdparm -W /dev/sda : off
virtio-scsi
---------------------
no cache defined : sdparm --get WCE /dev/sda : on
cache=none : sdparm --get WCE /dev/sda : on
cache=writeback : sdparm --get WCE /dev/sda : on
cache=writethrough : sdparm --get WCE /dev/sda : off
cache=directsync : sdparm --get WCE /dev/sda : off
lsi-scsi
---------------------
no cache defined : sdparm --get WCE /dev/sda : on
cache=none : sdparm --get WCE /dev/sda : on
cache=writeback : sdparm --get WCE /dev/sda : on
cache=writethrough : sdparm --get WCE /dev/sda : off
cache=directsync : sdparm --get WCE /dev/sda : off
virtio (guest kernel 3.6-rc4)
------------------------------
no cache defined : cat /sys/block/vda/cache_type : write_back
cache=none : cat /sys/block/vda/cache_type : : write_back
cache=writeback : cat /sys/block/vda/cache_type : write_back
cache=writethrough : cat /sys/block/vda/cache_type : write_through
cache=directsync : cat /sys/block/vda/cache_type : write_through
----- Mail original -----
De: "Alexandre DERUMIER" <aderum...@odiso.com>
À: pve-devel@pve.proxmox.com
Envoyé: Jeudi 6 Septembre 2012 13:38:58
Objet: Re: [pve-devel] qemu 1.2 :default cache mode writeback
firsts test (rc2)
qcow2 + ide
-----------
no cache defined : hdparm -W /dev/sda : off
cache=none : hdparm -W /dev/sda : on
cache=directsync : hdparm -W /dev/sda : off
cache=writethrough : hdparm -W /dev/sda : off
cache=writeback : hdparm -W /dev/sda : on
so the default mode seem to be writethrough or directsync ..??.
I'll do more tests with scsi disk, and also with kvm 1.1
----- Mail original -----
De: "Alexandre DERUMIER" <aderum...@odiso.com>
À: pve-devel@pve.proxmox.com
Envoyé: Jeudi 6 Septembre 2012 12:18:09
Objet: Re: [pve-devel] qemu 1.2 :default cache mode writeback
I have found the commit,
I'm not sure it's related to the host cache, but maybe more the cache inside
the guest ?
"Now all major device models (IDE, SCSI, virtio) can choose between
writethrough and writeback at run-time, and virtio will even revert
to writethrough if the guest is not capable of sending flushes. So
we can change the default to writeback at last.
Tested, for lack of a better idea, with a breakpoint on bdrv_open
and all cache choices one by one.
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
blockdev.c | 1 +
1 file modificato, 1 inserzione(+)
diff --git a/blockdev.c b/blockdev.c
index 8669142..7c83baa 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -377,6 +377,7 @@ DriveInfo *drive_init(QemuOpts *opts, int default_to_scsi)
}
}
+ bdrv_flags |= BDRV_O_CACHE_WB;
if ((buf = qemu_opt_get(opts, "cache")) != NULL) {
if (bdrv_parse_cache_flags(buf, &bdrv_flags) != 0) {
error_report("invalid cache option");
--
1.7.11.2
"
----- Mail original -----
De: "Alexandre DERUMIER" <aderum...@odiso.com>
À: pve-devel@pve.proxmox.com
Envoyé: Jeudi 6 Septembre 2012 12:13:48
Objet: [pve-devel] qemu 1.2 :default cache mode writeback
I just see that in the release note:
block: default cache mode is now writeback
Maybe do we need to warn proxmox users and update pve-manager ?
(default was cache=none if not defined)
_______________________________________________
pve-devel mailing list
pve-devel@pve.proxmox.com
http://pve.proxmox.com/cgi-bin/mailman/listinfo/pve-devel
_______________________________________________
pve-devel mailing list
pve-devel@pve.proxmox.com
http://pve.proxmox.com/cgi-bin/mailman/listinfo/pve-devel
_______________________________________________
pve-devel mailing list
pve-devel@pve.proxmox.com
http://pve.proxmox.com/cgi-bin/mailman/listinfo/pve-devel
_______________________________________________
pve-devel mailing list
pve-devel@pve.proxmox.com
http://pve.proxmox.com/cgi-bin/mailman/listinfo/pve-devel
