On Tue, May 08, 2018 at 06:40:23PM +0000, Moger, Babu wrote: > Hi Eduardo, One more comment below. > > > -----Original Message----- > > From: kvm-owner@xxxxxxxxxxxxxxx [mailto:kvm-owner@xxxxxxxxxxxxxxx] > > On Behalf Of Moger, Babu > > Sent: Monday, May 7, 2018 5:48 PM > > To: Eduardo Habkost <ehabkost@xxxxxxxxxx> > > Cc: geoff@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; mst@xxxxxxxxxx; > > kash@xxxxxxxxxxxxxx; mtosatti@xxxxxxxxxx; qemu-devel@xxxxxxxxxx; > > marcel@xxxxxxxxxx; pbonzini@xxxxxxxxxx; rth@xxxxxxxxxxx > > Subject: RE: [Qemu-devel] [PATCH v7 1/9] i386: Helpers to encode cache > > information consistently > > > > > > > > > -----Original Message----- > > > From: Eduardo Habkost [mailto:ehabkost@xxxxxxxxxx] > > > Sent: Monday, May 7, 2018 4:27 PM > > > To: Moger, Babu <Babu.Moger@xxxxxxx> > > > Cc: geoff@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; mst@xxxxxxxxxx; > > > kash@xxxxxxxxxxxxxx; mtosatti@xxxxxxxxxx; qemu-devel@xxxxxxxxxx; > > > marcel@xxxxxxxxxx; pbonzini@xxxxxxxxxx; rth@xxxxxxxxxxx > > > Subject: Re: [Qemu-devel] [PATCH v7 1/9] i386: Helpers to encode cache > > > information consistently > > > > > > On Mon, May 07, 2018 at 09:14:27PM +0000, Moger, Babu wrote: > > > > Eduardo, > > > > Thanks for all the comments. Will respond to each one separately. > > > > > > > > > -----Original Message----- > > > > > From: Eduardo Habkost [mailto:ehabkost@xxxxxxxxxx] > > > > > Sent: Monday, May 7, 2018 2:05 PM > > > > > To: Moger, Babu <Babu.Moger@xxxxxxx> > > > > > Cc: mst@xxxxxxxxxx; marcel@xxxxxxxxxx; pbonzini@xxxxxxxxxx; > > > > > rth@xxxxxxxxxxx; mtosatti@xxxxxxxxxx; geoff@xxxxxxxxxxxxxxx; > > > > > kash@xxxxxxxxxxxxxx; qemu-devel@xxxxxxxxxx; kvm@xxxxxxxxxxxxxxx > > > > > Subject: Re: [Qemu-devel] [PATCH v7 1/9] i386: Helpers to encode > > cache > > > > > information consistently > > > > > > > > > > Hi, > > > > > > > > > > I was about to apply this because I assumed it was the same patch > > > > > I sent in March, but then I found this: > > > > > > > > > > On Thu, Apr 26, 2018 at 11:26:41AM -0500, Babu Moger wrote: > > > > > > From: Eduardo Habkost <ehabkost@xxxxxxxxxx> > > > > > > > > > > > > Instead of having a collection of macros that need to be used in > > > > > > complex expressions to build CPUID data, define a CPUCacheInfo > > > > > > struct that can hold information about a given cache. Helper > > > > > > functions will take a CPUCacheInfo struct as input to encode > > > > > > CPUID leaves for a cache. > > > > > > > > > > > > This will help us ensure consistency between cache information > > > > > > CPUID leaves, and make the existing inconsistencies in CPUID info > > > > > > more visible. > > > > > > > > > > > > Signed-off-by: Eduardo Habkost <ehabkost@xxxxxxxxxx> > > > > > > Signed-off-by: Babu Moger <babu.moger@xxxxxxx> > > > > > > Tested-by: Geoffrey McRae <geoff@xxxxxxxxxxxxxxx> > > > > > [...] > > > > > > -#define L2_ASSOCIATIVITY 16 > > > > > [...] > > > > > > /*FIXME: CPUID leaf 0x80000006 is inconsistent with leaves 2 & 4 */ > > > > > > +static CPUCacheInfo l2_cache_amd = { > > > > > [...] > > > > > > + .associativity = 8, > > > > > [...] > > > > > > +}; > > > > > [...] > > > > > > case 0x80000006: > > > > > [...] > > > > > > - *ecx = (L2_SIZE_KB_AMD << 16) | \ > > > > > > - (AMD_ENC_ASSOC(L2_ASSOCIATIVITY) << 12) | \ > > > > > > - (L2_LINES_PER_TAG << 8) | (L2_LINE_SIZE); > > > > > [...] > > > > > > + encode_cache_cpuid80000006(&l2_cache_amd, > > > > > > + cpu->enable_l3_cache ? &l3_cache : NULL, > > > > > > + ecx, edx); > > > > > [...] > > > > > > > > > > The structs added by this patch are supposed to represent the > > > > > legacy cache sizes, and must match the old code. My original > > > > > patch set l2_cache_amd.associativity=16 because of that. > > > > > > > > > > This patch changes 0x80000006 from associativity=16 to > > > > > associativity=8. Why? > > Keeping this to 16 will be a problem. It breaks the size rule(line size *associativity * partitions * sets). > It asserts violating that rule. Now I remember. That is why I changed it to 8. I would think it would be > better to fix it now. You can fix it, no problem. You just need to make sure CPUID[0x80000006] data for old machine-types without topoext will stay the same. Remember that l2_cache_amd is just for the legacy values enabled by legacy-cache=on. Non-legacy values with more consistent data can be set at the CPU model table. The current CPUID data is: #define L2_SIZE_KB_AMD 512 #define L2_ASSOCIATIVITY 16 #define L2_LINES_PER_TAG 1 #define L2_LINE_SIZE 64 [...] case 0x80000006: *ecx = (L2_SIZE_KB_AMD << 16) | \ (AMD_ENC_ASSOC(L2_ASSOCIATIVITY) << 12) | \ (L2_LINES_PER_TAG << 8) | (L2_LINE_SIZE); This means l2_cache_amd.size must be 512KiB, l2_cache_amd.associativity must be 16, l2_cache_amd.lines_per_tag must be 1, and l2_cache_amd.line_size must be 64. l2_cache_amd.partitions and l2_cache_amd.sets, on the other hand, can be set to any value you wish. Another option is to simply disable CPUID[0x8000001d] if legacy-cache=on, so we don't need to worry about consistency on legacy cache entries that are known to be inconsistent. If we want to be extra safe/consistent, we can automatically set legacy-cache=off if topoext is enabled, and prevent QEMU from starting if topoext is enabled on a CPU without X86CPUDefinition.cache_info. We have lots of freedom on what to do when topoext is enabled or when using new machine-types. We just can't change the CPUID data of old machine-types when topoext is disabled. > > > > > > > > > The original code had a bug here. The associativity should have been 8. > > > > My earlier response from the thread > > > > http://patchwork.ozlabs.org/patch/884880/ > > > > > > > > This should have been 8-way. This is a bug. Will fix. > > > > This should have been (AMD_ENC_ASSOC(L2_ASSOCIATIVITY_AMD) << > > > 12) > > > > > > If we want to change the associativity, we must keep the old > > > values on older machine-types, which was the whole purpose of the > > > "legacy-cache" property. > > > > > > I suggest using the new X86CPUDefinition::cache_info field if you > > > want to make AMD CPUs report different associativity. > > > > Ok. Sure. I will change it. Thanks > > > > > > > > -- > > > Eduardo -- Eduardo
