powerpc/kexec: Speedup kexec hash PTE tear down

powerpc/kexec: Speedup kexec hash PTE tear down

Commit: d504bed676caad29a3dba3d3727298c560628f5c upstream

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.

---
 arch/powerpc/platforms/pseries/lpar.c |   33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

Index: b/arch/powerpc/platforms/pseries/lpar.c
===================================================================
@@ -366,21 +366,28 @@
 {

	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));
		}
	}

}