pmap_invalidate_range: For very large ranges, flush the whole TLB

Typical TLBs have 40-512 entries available.  At some point, iterating
every single page in a requested invalidation range and issuing invlpg
on it is more expensive than flushing the TLB and allowing it to reload
on demand.

Broadwell CPUs have 1536 L2 TLB entries, so I've picked the arbitrary
number 4096 entries as a hueristic at which point we flush TLB rather
than invalidating every single potential page.

Reviewed by:	alc
Feedback from:	jhb, kib
MFC notes:	Depends on r291688
Sponsored by:	EMC / Isilon Storage Division
Differential Revision:	https://reviews.freebsd.org/D4280

1 files changed, 8 insertions, 0 deletions

diff --git a/sys/i386/i386/pmap.c b/sys/i386/i386/pmap.c
index 5ae41a316deb..5bdc98875ca7 100644
--- a/sys/i386/i386/pmap.c
+++ b/sys/i386/i386/pmap.c
@@ -1032,6 +1032,9 @@ pmap_invalidate_page(pmap_t pmap, vm_offset_t va)
 	sched_unpin();
 }
 
+/* 4k PTEs -- Chosen to exceed the total size of Broadwell L2 TLB */
+#define	PMAP_INVLPG_THRESHOLD	(4 * 1024 * PAGE_SIZE)
+
 void
 pmap_invalidate_range(pmap_t pmap, vm_offset_t sva, vm_offset_t eva)
 {
@@ -1039,6 +1042,11 @@ pmap_invalidate_range(pmap_t pmap, vm_offset_t sva, vm_offset_t eva)
 	vm_offset_t addr;
 	u_int cpuid;
 
+	if (eva - sva >= PMAP_INVLPG_THRESHOLD) {
+		pmap_invalidate_all(pmap);
+		return;
+	}
+
 	sched_pin();
 	if (pmap == kernel_pmap || !CPU_CMP(&pmap->pm_active, &all_cpus)) {
 		for (addr = sva; addr < eva; addr += PAGE_SIZE)