On 2015-04-20 19:16, Radim Krčmář wrote:
> 2015-04-20 18:14+0200, Radim Krčmář:
>> Tested-by: Radim Krčmář <rkrcmar@xxxxxxxxxx>
>
> 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
--
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux
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