Date: Sat, 10 Jul 2010 18:22:44 +0000 (UTC) From: Alan Cox <alc@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r209887 - in head/sys: amd64/amd64 i386/i386 Message-ID: <201007101822.o6AIMjnG032398@svn.freebsd.org>
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Author: alc Date: Sat Jul 10 18:22:44 2010 New Revision: 209887 URL: http://svn.freebsd.org/changeset/base/209887 Log: Reduce the number of global TLB shootdowns generated by pmap_qenter(). Specifically, teach pmap_qenter() to recognize the case when it is being asked to replace a mapping with the very same mapping and not generate a shootdown. Unfortunately, the buffer cache commonly passes an entire buffer to pmap_qenter() when only a subset of the mappings are changing. For the extension of buffers in allocbuf() this was resulting in unnecessary shootdowns. The addition of new pages to the end of the buffer need not and did not trigger a shootdown, but overwriting the initial mappings with the very same mappings was seen as a change that necessitated a shootdown. With this change, that is no longer so. For a "buildworld" on amd64, this change eliminates 14-15% of the pmap_invalidate_range() shootdowns, and about 4% of the overall shootdowns. MFC after: 3 weeks Modified: head/sys/amd64/amd64/pmap.c head/sys/i386/i386/pmap.c Modified: head/sys/amd64/amd64/pmap.c ============================================================================== --- head/sys/amd64/amd64/pmap.c Sat Jul 10 17:46:53 2010 (r209886) +++ head/sys/amd64/amd64/pmap.c Sat Jul 10 18:22:44 2010 (r209887) @@ -1331,19 +1331,22 @@ pmap_map(vm_offset_t *virt, vm_paddr_t s void pmap_qenter(vm_offset_t sva, vm_page_t *ma, int count) { - pt_entry_t *endpte, oldpte, *pte; + pt_entry_t *endpte, oldpte, pa, *pte; + vm_page_t m; oldpte = 0; pte = vtopte(sva); endpte = pte + count; while (pte < endpte) { - oldpte |= *pte; - pte_store(pte, VM_PAGE_TO_PHYS(*ma) | PG_G | - pmap_cache_bits((*ma)->md.pat_mode, 0) | PG_RW | PG_V); + m = *ma++; + pa = VM_PAGE_TO_PHYS(m) | pmap_cache_bits(m->md.pat_mode, 0); + if ((*pte & (PG_FRAME | PG_PTE_CACHE)) != pa) { + oldpte |= *pte; + pte_store(pte, pa | PG_G | PG_RW | PG_V); + } pte++; - ma++; } - if ((oldpte & PG_V) != 0) + if (__predict_false((oldpte & PG_V) != 0)) pmap_invalidate_range(kernel_pmap, sva, sva + count * PAGE_SIZE); } Modified: head/sys/i386/i386/pmap.c ============================================================================== --- head/sys/i386/i386/pmap.c Sat Jul 10 17:46:53 2010 (r209886) +++ head/sys/i386/i386/pmap.c Sat Jul 10 18:22:44 2010 (r209887) @@ -1461,19 +1461,22 @@ pmap_map(vm_offset_t *virt, vm_paddr_t s void pmap_qenter(vm_offset_t sva, vm_page_t *ma, int count) { - pt_entry_t *endpte, oldpte, *pte; + pt_entry_t *endpte, oldpte, pa, *pte; + vm_page_t m; oldpte = 0; pte = vtopte(sva); endpte = pte + count; while (pte < endpte) { - oldpte |= *pte; - pte_store(pte, VM_PAGE_TO_PHYS(*ma) | pgeflag | - pmap_cache_bits((*ma)->md.pat_mode, 0) | PG_RW | PG_V); + m = *ma++; + pa = VM_PAGE_TO_PHYS(m) | pmap_cache_bits(m->md.pat_mode, 0); + if ((*pte & (PG_FRAME | PG_PTE_CACHE)) != pa) { + oldpte |= *pte; + pte_store(pte, pa | pgeflag | PG_RW | PG_V); + } pte++; - ma++; } - if ((oldpte & PG_V) != 0) + if (__predict_false((oldpte & PG_V) != 0)) pmap_invalidate_range(kernel_pmap, sva, sva + count * PAGE_SIZE); }
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