powerpc/kexec: Speedup kexec hash PTE tear down

Currently for kexec the PTE tear down on 1TB segment systems normally
requires 3 hcalls for each PTE removal. On a machine with 32GB of
memory it can take around a minute to remove all the PTEs.

This optimises the path so that we only remove PTEs that are valid.
It also uses the read 4 PTEs at once HCALL.  For the common case where
a PTEs is invalid in a 1TB segment, this turns the 3 HCALLs per PTE
down to 1 HCALL per 4 PTEs.

This gives an > 10x speedup in kexec times on PHYP, taking a 32GB
machine from around 1 minute down to a few seconds.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index 0707653..cf79b46 100644 (file)
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -367,21 +367,28 @@ static void pSeries_lpar_hptab_clear(void)
 {
        unsigned long size_bytes = 1UL << ppc64_pft_size;
        unsigned long hpte_count = size_bytes >> 4;
-       unsigned long dummy1, dummy2, dword0;
+       struct {
+               unsigned long pteh;
+               unsigned long ptel;
+       } ptes[4];
        long lpar_rc;
-       int i;
+       int i, j;
 
-       /* TODO: Use bulk call */
-       for (i = 0; i < hpte_count; i++) {
-               /* dont remove HPTEs with VRMA mappings */
-               lpar_rc = plpar_pte_remove_raw(H_ANDCOND, i, HPTE_V_1TB_SEG,
-                                               &dummy1, &dummy2);
-               if (lpar_rc == H_NOT_FOUND) {
-                       lpar_rc = plpar_pte_read_raw(0, i, &dword0, &dummy1);
-                       if (!lpar_rc && ((dword0 & HPTE_V_VRMA_MASK)
-                               != HPTE_V_VRMA_MASK))
-                               /* Can be hpte for 1TB Seg. So remove it */
-                               plpar_pte_remove_raw(0, i, 0, &dummy1, &dummy2);
+       /* Read in batches of 4,
+        * invalidate only valid entries not in the VRMA
+        * hpte_count will be a multiple of 4
+         */
+       for (i = 0; i < hpte_count; i += 4) {
+               lpar_rc = plpar_pte_read_4_raw(0, i, (void *)ptes);
+               if (lpar_rc != H_SUCCESS)
+                       continue;
+               for (j = 0; j < 4; j++){
+                       if ((ptes[j].pteh & HPTE_V_VRMA_MASK) ==
+                               HPTE_V_VRMA_MASK)
+                               continue;
+                       if (ptes[j].pteh & HPTE_V_VALID)
+                               plpar_pte_remove_raw(0, i + j, 0,
+                                       &(ptes[j].pteh), &(ptes[j].ptel));
                }
        }
 }