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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] xen-unstable, winxp32 very poor performance on AMD FX-8150, I bisected and changeset is 24770:7f79475d3de7
On 2012-11-01 18:28, Andres Lagar-Cavilla wrote:
> On Nov 1, 2012, at 1:00 PM, Tim Deegan <tim@xxxxxxx> wrote:
>
>> Hi,
>>
>> At 14:59 +0100 on 22 Oct (1350917960), Tim Deegan wrote:
>>> At 19:21 +0200 on 20 Oct (1350760876), Peter Maloney wrote:
>>>> The change was 8 months ago
>>>>
>>>> changeset: 24770:7f79475d3de7
>>>> user: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
>>>> date: Fri Feb 10 16:07:07 2012 +0000
>>>> summary: x86/mm: Make p2m lookups fully synchronized wrt modifications
>>> This change was bad for performnace across the board and most of it has
>>> since been either reverted or amended, but clearly we missed something
>>> here.
>>>
>>> It's interesting that Win8 isn't slowed down. I wonder whether that's to
>>> do with the way it drives the VGA card -- IIRC it uses a generic VESA
>>> driver rather than a Cirrus one.
>> In fact this is to do with the APIC. On my test system, a busy 2-vcpu
>> VM is making about 300k/s accesses to the APIC TPR. These accesses are
>> all trapped and emulated by Xen, and that emulation has got more
>> expensive as part of this change.
>>
>> Later Windows OSes have a feature called 'lazy IRQL' which makes those
>> accesses go away, but sadly that's not been done for WinXP. On modern
>> Intel CPUs, the hardware acceleration for TPR accesses works for XP; on
>> AMD it requires the OS to use 'MOV reg32, CR8' to access the TPR instead
>> of MMIO, which XP is clearly not doing. :(
>>
>> Peter: if you have the option, you might find that installing the PV
>> drivers that ship with Citrix XenServer 6.0 makes things work better.
>>
>> Andres: even though this load of APIC emulations is pretty extreme, it's
>> surprising that the VM runs faster on shadow pagetables! Any ideas for
>> where this slowdown is coming from?
> Not any immediate ideas without profiling.
>
> However, most callers of hvmemul_do_io pass a stub zero ram_gpa address. We
> might be madly hitting the p2m locks for no reason there.
>
> How about the following patch, Peter, Tim?
Thanks,
I'll give it a try sometime this week I guess.
> diff -r 5171750d133e xen/arch/x86/hvm/emulate.c
> --- a/xen/arch/x86/hvm/emulate.c
> +++ b/xen/arch/x86/hvm/emulate.c
> @@ -60,24 +60,28 @@ static int hvmemul_do_io(
> ioreq_t *p = get_ioreq(curr);
> unsigned long ram_gfn = paddr_to_pfn(ram_gpa);
> p2m_type_t p2mt;
> - struct page_info *ram_page;
> + struct page_info *ram_page = NULL;
> int rc;
>
> /* Check for paged out page */
> - ram_page = get_page_from_gfn(curr->domain, ram_gfn, &p2mt, P2M_UNSHARE);
> - if ( p2m_is_paging(p2mt) )
> + if ( ram_gpa != INVALID_MFN )
> {
> - if ( ram_page )
> - put_page(ram_page);
> - p2m_mem_paging_populate(curr->domain, ram_gfn);
> - return X86EMUL_RETRY;
> - }
> - if ( p2m_is_shared(p2mt) )
> - {
> - if ( ram_page )
> - put_page(ram_page);
> - return X86EMUL_RETRY;
> - }
> + ram_page = get_page_from_gfn(curr->domain, ram_gfn, &p2mt,
> P2M_UNSHARE);
> + if ( p2m_is_paging(p2mt) )
> + {
> + if ( ram_page )
> + put_page(ram_page);
> + p2m_mem_paging_populate(curr->domain, ram_gfn);
> + return X86EMUL_RETRY;
> + }
> + if ( p2m_is_shared(p2mt) )
> + {
> + if ( ram_page )
> + put_page(ram_page);
> + return X86EMUL_RETRY;
> + }
> + } else
> + value = 0; /* for pvalue */
>
> /*
> * Weird-sized accesses have undefined behaviour: we discard writes
> @@ -455,7 +459,7 @@ static int __hvmemul_read(
> return X86EMUL_UNHANDLEABLE;
> gpa = (((paddr_t)vio->mmio_gpfn << PAGE_SHIFT) | off);
> if ( (off + bytes) <= PAGE_SIZE )
> - return hvmemul_do_mmio(gpa, &reps, bytes, 0,
> + return hvmemul_do_mmio(gpa, &reps, bytes, INVALID_MFN,
> IOREQ_READ, 0, p_data);
> }
>
> @@ -480,7 +484,8 @@ static int __hvmemul_read(
> addr, &gpa, bytes, &reps, pfec, hvmemul_ctxt);
> if ( rc != X86EMUL_OKAY )
> return rc;
> - return hvmemul_do_mmio(gpa, &reps, bytes, 0, IOREQ_READ, 0, p_data);
> + return hvmemul_do_mmio(gpa, &reps, bytes, INVALID_MFN,
> + IOREQ_READ, 0, p_data);
> case HVMCOPY_gfn_paged_out:
> return X86EMUL_RETRY;
> case HVMCOPY_gfn_shared:
> @@ -552,7 +557,7 @@ static int hvmemul_write(
> unsigned int off = addr & (PAGE_SIZE - 1);
> gpa = (((paddr_t)vio->mmio_gpfn << PAGE_SHIFT) | off);
> if ( (off + bytes) <= PAGE_SIZE )
> - return hvmemul_do_mmio(gpa, &reps, bytes, 0,
> + return hvmemul_do_mmio(gpa, &reps, bytes, INVALID_MFN,
> IOREQ_WRITE, 0, p_data);
> }
>
> @@ -573,7 +578,7 @@ static int hvmemul_write(
> addr, &gpa, bytes, &reps, pfec, hvmemul_ctxt);
> if ( rc != X86EMUL_OKAY )
> return rc;
> - return hvmemul_do_mmio(gpa, &reps, bytes, 0,
> + return hvmemul_do_mmio(gpa, &reps, bytes, INVALID_MFN,
> IOREQ_WRITE, 0, p_data);
> case HVMCOPY_gfn_paged_out:
> return X86EMUL_RETRY;
> @@ -804,7 +809,7 @@ static int hvmemul_read_io(
> {
> unsigned long reps = 1;
> *val = 0;
> - return hvmemul_do_pio(port, &reps, bytes, 0, IOREQ_READ, 0, val);
> + return hvmemul_do_pio(port, &reps, bytes, INVALID_MFN, IOREQ_READ, 0,
> val);
> }
>
> static int hvmemul_write_io(
> @@ -814,7 +819,7 @@ static int hvmemul_write_io(
> struct x86_emulate_ctxt *ctxt)
> {
> unsigned long reps = 1;
> - return hvmemul_do_pio(port, &reps, bytes, 0, IOREQ_WRITE, 0, &val);
> + return hvmemul_do_pio(port, &reps, bytes, INVALID_MFN, IOREQ_WRITE, 0,
> &val);
> }
>
> static int hvmemul_read_cr(
> diff -r 5171750d133e xen/arch/x86/hvm/io.c
> --- a/xen/arch/x86/hvm/io.c
> +++ b/xen/arch/x86/hvm/io.c
> @@ -231,7 +231,7 @@ int handle_pio(uint16_t port, int size,
> if ( dir == IOREQ_WRITE )
> data = guest_cpu_user_regs()->eax;
>
> - rc = hvmemul_do_pio(port, &reps, size, 0, dir, 0, &data);
> + rc = hvmemul_do_pio(port, &reps, size, INVALID_MFN, dir, 0, &data);
>
> switch ( rc )
> {
>
>
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