[libvirt] [PATCH v2 1/3] qemu_domain: simplify non-VFIO memLockLimit calc for PPC64

Daniel Henrique Barboza danielhb413 at gmail.com
Sun Mar 3 13:23:12 UTC 2019


passthroughLimit is being calculated even if usesVFIO is false.
After that, a if/else conditional is used to check if we're going
to sum it up with baseLimit.

This patch initializes passthroughLimit to zero and always
return memKB = baseLimit + passthroughLimit. The conditional
is then used to calculate passthroughLimit if usesVFIO is true.
This results in some cycles spared for the usesVFIO=false
scenario, but the real motivation is to make the code simpler
to add an alternative passthroughLimit formula for NVLink2
passthrough.

Signed-off-by: Daniel Henrique Barboza <danielhb413 at gmail.com>
---
 src/qemu/qemu_domain.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 59fe1eb401..55578f3d19 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -10366,7 +10366,7 @@ qemuDomainGetMemLockLimitBytes(virDomainDefPtr def)
         unsigned long long maxMemory;
         unsigned long long memory;
         unsigned long long baseLimit;
-        unsigned long long passthroughLimit;
+        unsigned long long passthroughLimit = 0;
         size_t nPCIHostBridges = 0;
         bool usesVFIO = false;
 
@@ -10432,15 +10432,12 @@ qemuDomainGetMemLockLimitBytes(virDomainDefPtr def)
          * kiB pages, less still if the guest is mapped with hugepages (unlike
          * the default 32-bit DMA window, DDW windows can use large IOMMU
          * pages). 8 MiB is for second and further level overheads, like (b) */
-        passthroughLimit = MAX(2 * 1024 * 1024 * nPCIHostBridges,
-                               memory +
-                               memory / 512 * nPCIHostBridges + 8192);
-
         if (usesVFIO)
-            memKB = baseLimit + passthroughLimit;
-        else
-            memKB = baseLimit;
+            passthroughLimit = MAX(2 * 1024 * 1024 * nPCIHostBridges,
+                                   memory +
+                                   memory / 512 * nPCIHostBridges + 8192);
 
+        memKB = baseLimit + passthroughLimit;
         goto done;
     }
 
-- 
2.20.1




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