On Wed, Jan 31, 2024 at 04:59:29PM +0100, Alexandre Ghiti wrote: > The preventive sfence.vma were emitted because new mappings must be made > visible to the page table walker but Svvptc guarantees that xRET act as > a fence, so no need to sfence.vma for the uarchs that implement this > extension. AFAIU, your first submission shows that you don't need that xRET property. Similarly for other archs. What was rationale behind this Svvptc change? > This allows to drastically reduce the number of sfence.vma emitted: > > * Ubuntu boot to login: > Before: ~630k sfence.vma > After: ~200k sfence.vma > > * ltp - mmapstress01 > Before: ~45k > After: ~6.3k > > * lmbench - lat_pagefault > Before: ~665k > After: 832 (!) > > * lmbench - lat_mmap > Before: ~546k > After: 718 (!) This Svvptc seems to move/add the "burden" of the synchronization to xRET: Perhaps integrate the above counts w/ the perf gains in the cover letter? Andrea
