Date: Fri, 6 Apr 2012 16:41:19 +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: r233954 - head/sys/amd64/amd64 Message-ID: <201204061641.q36GfJkI017531@svn.freebsd.org>
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Author: alc Date: Fri Apr 6 16:41:19 2012 New Revision: 233954 URL: http://svn.freebsd.org/changeset/base/233954 Log: Micro-optimize free_pv_entry() for the expected case. Modified: head/sys/amd64/amd64/pmap.c Modified: head/sys/amd64/amd64/pmap.c ============================================================================== --- head/sys/amd64/amd64/pmap.c Fri Apr 6 16:32:29 2012 (r233953) +++ head/sys/amd64/amd64/pmap.c Fri Apr 6 16:41:19 2012 (r233954) @@ -2095,7 +2095,6 @@ pmap_collect(pmap_t locked_pmap, struct } } - /* * free the pv_entry back to the free list */ @@ -2116,13 +2115,16 @@ free_pv_entry(pmap_t pmap, pv_entry_t pv field = idx / 64; bit = idx % 64; pc->pc_map[field] |= 1ul << bit; - /* move to head of list */ - TAILQ_REMOVE(&pmap->pm_pvchunk, pc, pc_list); if (pc->pc_map[0] != PC_FREE0 || pc->pc_map[1] != PC_FREE1 || pc->pc_map[2] != PC_FREE2) { - TAILQ_INSERT_HEAD(&pmap->pm_pvchunk, pc, pc_list); + /* 98% of the time, pc is already at the head of the list. */ + if (__predict_false(pc != TAILQ_FIRST(&pmap->pm_pvchunk))) { + TAILQ_REMOVE(&pmap->pm_pvchunk, pc, pc_list); + TAILQ_INSERT_HEAD(&pmap->pm_pvchunk, pc, pc_list); + } return; } + TAILQ_REMOVE(&pmap->pm_pvchunk, pc, pc_list); PV_STAT(pv_entry_spare -= _NPCPV); PV_STAT(pc_chunk_count--); PV_STAT(pc_chunk_frees++);
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