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Re: [Xen-devel] Xen 4.3 development update
On 04/05/13 11:47, Pasi Kärkkäinen wrote:
On Fri, May 03, 2013 at 05:41:35PM +0100, George Dunlap wrote:
On 02/05/13 16:48, Tim Deegan wrote:
At 15:21 +0200 on 29 Apr (1367248894), Peter Maloney wrote:
On 04/04/2013 07:05 PM, Tim Deegan wrote:
Also, if there is still a bad slowdown, caused by the p2m lookups, this
might help a little bit:
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 38e87ce..7bd8646 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -1361,6 +1361,18 @@ int hvm_hap_nested_page_fault(paddr_t gpa,
}
}
+
+ /* For the benefit of 32-bit WinXP (& older Windows) on AMD CPUs,
+ * a fast path for LAPIC accesses, skipping the p2m lookup. */
+ if ( !nestedhvm_vcpu_in_guestmode(v)
+ && gfn == vlapic_base_address(vcpu_vlapic(current)) >> PAGE_SHIFT )
+ {
+ if ( !handle_mmio() )
+ hvm_inject_hw_exception(TRAP_gp_fault, 0);
+ rc = 1;
+ goto out;
+ }
+
p2m = p2m_get_hostp2m(v->domain);
mfn = get_gfn_type_access(p2m, gfn, &p2mt, &p2ma,
P2M_ALLOC | (access_w ? P2M_UNSHARE : 0), NULL);
This patch (applied to 4.2.2) has a very large improvement on my box
(AMD FX-8150) and WinXP 32 bit.
Hmm - I expected it to be only a mild improvement. How about this one,
which puts in the same shortcut in another place as well? I don't think
it will be much better than the last one, but it's worth a try.
So I dusted off my old perf testing scripts and added in one to
measure boot performance.
Below are boot times, from after "xl create" returns, until a
specific python daemon running in the VM starts responding to
requests. So lower is better.
There are a number of places where there can be a few seconds of
noise either way, but on the whole the tests seem fairly repeatable.
I ran this with w2k3eesp2 and with winxpsp3, using some of the
auto-install test images made for the XenServer regression testing.
All of them are using a flat file disk backend with
qemu-traditional.
Results are in order of commits:
Xen 4.1:
w2k3: 43 34 34 33 34
winxp: 110 111 111 110 112
Xen 4.2:
w2k3: 34 44 45 45 45
winxp: 203 221 210 211 200
Xen-unstable w/ RTC fix:
w2k3: 43 44 44 45 44
winxp: 268 275 265 276 265
Xen-unstable with rtc fix + this "fast lapic" patch:
w2k3: 43 45 44 45 45
winxp: 224 232 232 232 232
So w2k3 boots fairly quickly anyway; has a 50% slow-down when moving
from 4.1 to 4.2, and no discernible change after that.
winxp boots fairly slowly; nearly doubles in speed for 4.2, and gets
even worse for xen-unstable. The patch is a measurable improvement,
but still nowhere near 4.1, or even 4.2.
On the whole however -- I'm not sure that boot time by itself is a
blocker. If the problem really is primarily the "eager TPR" issue
for Windows XP, then I'm not terribly motivated either: the Citrix
PV drivers patch Windows XP to modify the routine to be lazy (like
w2k3); there is hardware available which allows the TPR to be
virtualized; and there are plenty of Windows-based OSes available
which do not have this problem.
A couple of questions:
- Does Citrix XenServer Windows PV driver work with vanilla Xen 4.2.x? I
remember someone complaining on the list that it doesn't work.. (but I'm not
sure about that).
I did a quick test of the XS 6.0.2 drivers on unstable and they didn't
work. Didn't do any debugging, however.
- Does GPLPV do the lazy patching for WinXP on AMD?
I highly doubt it, but you'd have to ask James Harper.
-George
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