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Subject[10/17] powerpc/kexec: Speedup kexec hash PTE tear down
2.6.32-longterm review patch.  If anyone has any objections, please let us know.

------------------

From: Michael Neuling <mikey@neuling.org>

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.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Kamalesh babulal <kamalesh@linux.vnet.ibm.com>
cc: Anton Blanchard <anton@samba.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

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

--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -366,21 +366,28 @@ static void pSeries_lpar_hptab_clear(voi
{
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));
}
}
}



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