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authorDavid Gibson <david@gibson.dropbear.id.au>2012-09-20 17:42:27 +0000
committerAlexander Graf <agraf@suse.de>2012-10-04 15:54:18 +0200
commit382be75df77142cf6bdc7f5852738029eeb9e23a (patch)
treed60dfdc6c089f97ee965cb42d7488ea5164f95af
parent35f9304d925a5423c51bd2c83a81fa3cc2b6e680 (diff)
pseries: Set hash table size based on RAM size
Currently the pseries machine code always attempts to set the size of the guests's hash page table to 16MB. However, because of the way the POWER MMU works, a suitable hash page table size should really depend on memory size. 16MB will be excessive for guests with <1GB and RAM, and may not be enough for guests with >2GB of RAM (depending on guest page size and other factors). The usual given rule of thumb is that the hash table should be 1/64 of the size of memory, but in fact the Linux guests we are aiming at don't really need that much. This patch, therefore, changes the hash table allocation code to aim for 1/128 of the size of RAM (rounding up). When using KVM, this size may still be adjusted by the host kernel if it is unable to allocate a suitable (contiguous) table. Signed-off-by: David Gibson <david@gibson.dropbear.id.au> Signed-off-by: Alexander Graf <agraf@suse.de>
-rw-r--r--hw/spapr.c13
1 files changed, 10 insertions, 3 deletions
diff --git a/hw/spapr.c b/hw/spapr.c
index 1177efaa98..a8bd3c1ae6 100644
--- a/hw/spapr.c
+++ b/hw/spapr.c
@@ -725,9 +725,16 @@ static void ppc_spapr_init(ram_addr_t ram_size,
spapr->fdt_addr = spapr->rtas_addr - FDT_MAX_SIZE;
load_limit = spapr->fdt_addr - FW_OVERHEAD;
- /* For now, always aim for a 16MB hash table */
- /* FIXME: we should change this default based on RAM size */
- spapr->htab_shift = 24;
+ /* We aim for a hash table of size 1/128 the size of RAM. The
+ * normal rule of thumb is 1/64 the size of RAM, but that's much
+ * more than needed for the Linux guests we support. */
+ spapr->htab_shift = 18; /* Minimum architected size */
+ while (spapr->htab_shift <= 46) {
+ if ((1ULL << (spapr->htab_shift + 7)) >= ram_size) {
+ break;
+ }
+ spapr->htab_shift++;
+ }
/* init CPUs */
if (cpu_model == NULL) {