Date: Sat, 24 Jul 2021 18:10:04 GMT From: Alan Cox <alc@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 3687797618b6 - main - amd64: Don't repeat unnecessary tests when cmpset fails Message-ID: <202107241810.16OIA4bx009124@gitrepo.freebsd.org>
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The branch main has been updated by alc: URL: https://cgit.FreeBSD.org/src/commit/?id=3687797618b6c978ad733bd206a623e5df47dbe3 commit 3687797618b6c978ad733bd206a623e5df47dbe3 Author: Alan Cox <alc@FreeBSD.org> AuthorDate: 2021-07-24 08:50:27 +0000 Commit: Alan Cox <alc@FreeBSD.org> CommitDate: 2021-07-24 18:06:47 +0000 amd64: Don't repeat unnecessary tests when cmpset fails When a cmpset for removing the PG_RW bit in pmap_promote_pde() fails, there is no need to repeat the alignment, PG_A, and PG_V tests just to reload the PTE's value. The only bit that we need be concerned with at this point is PG_M. Use fcmpset instead. MFC after: 1 week --- sys/amd64/amd64/pmap.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c index aea4394ebcc0..47315c560831 100644 --- a/sys/amd64/amd64/pmap.c +++ b/sys/amd64/amd64/pmap.c @@ -6615,7 +6615,6 @@ pmap_promote_pde(pmap_t pmap, pd_entry_t *pde, vm_offset_t va, * within a 2MB page. */ firstpte = (pt_entry_t *)PHYS_TO_DMAP(*pde & PG_FRAME); -setpde: newpde = *firstpte; if ((newpde & ((PG_FRAME & PDRMASK) | PG_A | PG_V)) != (PG_A | PG_V) || !pmap_allow_2m_x_page(pmap, pmap_pde_ept_executable(pmap, @@ -6625,12 +6624,13 @@ setpde: " in pmap %p", va, pmap); return; } +setpde: if ((newpde & (PG_M | PG_RW)) == PG_RW) { /* * When PG_M is already clear, PG_RW can be cleared without * a TLB invalidation. */ - if (!atomic_cmpset_long(firstpte, newpde, newpde & ~PG_RW)) + if (!atomic_fcmpset_long(firstpte, &newpde, newpde & ~PG_RW)) goto setpde; newpde &= ~PG_RW; } @@ -6642,7 +6642,6 @@ setpde: */ pa = (newpde & (PG_PS_FRAME | PG_A | PG_V)) + NBPDR - PAGE_SIZE; for (pte = firstpte + NPTEPG - 1; pte > firstpte; pte--) { -setpte: oldpte = *pte; if ((oldpte & (PG_FRAME | PG_A | PG_V)) != pa) { counter_u64_add(pmap_pde_p_failures, 1); @@ -6650,12 +6649,13 @@ setpte: " in pmap %p", va, pmap); return; } +setpte: if ((oldpte & (PG_M | PG_RW)) == PG_RW) { /* * When PG_M is already clear, PG_RW can be cleared * without a TLB invalidation. */ - if (!atomic_cmpset_long(pte, oldpte, oldpte & ~PG_RW)) + if (!atomic_fcmpset_long(pte, &oldpte, oldpte & ~PG_RW)) goto setpte; oldpte &= ~PG_RW; CTR2(KTR_PMAP, "pmap_promote_pde: protect for va %#lx"
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