Re: [RFC][PATCH] KVM: SVM: Sync g_pat with guest-written PAT value

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2015-04-20 19:16, Radim Krčmář wrote:
> 2015-04-20 18:14+0200, Radim Krčmář:
>> Tested-by: Radim Krčmář <rkrcmar@redhat.com>
> 
> Uncached accesses were roughly 20x slower.
> In case anyone wanted to reproduce, I used this as a kvm-unit-test:
> 
> ---
> #include "processor.h"
> 
> #define NR_TOP_LOOPS 24
> #define NR_MEM_LOOPS 10
> #define MEM_ELEMENTS 1024
> 
> static volatile u64 pat_test_memory[MEM_ELEMENTS];
> 
> static void flush_tlb(void)
> {
> 	write_cr3(read_cr3());
> }
> 
> static void set_pat(u64 val)
> {
> 	wrmsr(0x277, val);
> 	flush_tlb();
> 
> }
> 
> static u64 time_memory_accesses(void)
> {
> 	u64 tsc_before = rdtsc();
> 
> 	for (unsigned loop = 0; loop < NR_MEM_LOOPS; loop++)
> 		for (unsigned i = 0; i < MEM_ELEMENTS; i++)
> 			pat_test_memory[i]++;
> 
> 	return rdtsc() - tsc_before;
> }
> 
> int main(int argc, char **argv)
> {
> 	unsigned error = 0;
> 
> 	for (unsigned loop = 0; loop < NR_TOP_LOOPS; loop++) {
> 		u64 time_uc, time_wb;
> 
> 		set_pat(0);
> 		time_uc = time_memory_accesses();
> 
> 		set_pat(0x0606060606060606ULL);
> 		time_wb = time_memory_accesses();
> 
> 		if (time_uc < time_wb * 4)
> 			error++;
> 
> 		printf("%02d uc: %10lld wb: %8lld\n", loop, time_uc, time_wb);
> 	}
> 
> 	report("guest PAT", !error);
> 
> 	return report_summary();
> }
> 

Great, thanks. Will you push it to the unit tests? Could raise
motivations to fix the !NPT/EPT case.

Jan

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