pseries: Add helper to calculate recommended hash page table size
At present we calculate the recommended hash page table (HPT) size for a
pseries guest just once in ppc_spapr_init() before allocating the HPT.
In future patches we're going to want this calculation in other places, so
this splits it out into a helper function. While we're at it, change the
calculation to use ctz() instead of an explicit loop.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index c315715..2a81e8f 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -1050,6 +1050,19 @@
spapr->htab_fd = -1;
}
+static int spapr_hpt_shift_for_ramsize(uint64_t ramsize)
+{
+ int shift;
+
+ /* We aim for a hash table of size 1/128 the size of RAM (rounded
+ * up). The PAPR recommendation is actually 1/64 of RAM size, but
+ * that's much more than is needed for Linux guests */
+ shift = ctz64(pow2ceil(ramsize)) - 7;
+ shift = MAX(shift, 18); /* Minimum architected size */
+ shift = MIN(shift, 46); /* Maximum architected size */
+ return shift;
+}
+
static void spapr_alloc_htab(sPAPRMachineState *spapr)
{
long shift;
@@ -1790,16 +1803,7 @@
/* Setup a load limit for the ramdisk leaving room for SLOF and FDT */
load_limit = MIN(spapr->rma_size, RTAS_MAX_ADDR) - FW_OVERHEAD;
- /* 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)) >= machine->maxram_size) {
- break;
- }
- spapr->htab_shift++;
- }
+ spapr->htab_shift = spapr_hpt_shift_for_ramsize(machine->maxram_size);
spapr_alloc_htab(spapr);
/* Set up Interrupt Controller before we create the VCPUs */
