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authorRafał Miłecki <rafal@milecki.pl>2022-07-03 13:22:00 +0200
committerRafał Miłecki <rafal@milecki.pl>2022-07-08 16:18:25 +0200
commitb54ef39e0b910a4b8eaca0497fe9b63e8392262a (patch)
treeb9ed5ba53325ebdfc918af0f5b3d62d6b94f6d0e
parenta50f5b3fb2024fe00f726dff2093a83410bd3c8d (diff)
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bcm53xx: use -falign-functions=32 for kernel compilation
Northstar SoCs have pretty small CPU caches and their performance is heavily affected by cache hits & misses. It means that all kind of random code changes can affect performance as they often reorganize (change alignment & possibly reorder) kernel symbols. It was discussed in ARM / net mailinglists: 1. ARM router NAT performance affected by random/unrelated commits [1] [2] 2. Optimizing kernel compilation / alignments for network performance [3] [4] It seems that -falign-functions can be used as a partial workaround. It doesn't solve all cases (e.g. documented watchdog one [5]) but it surely helps with many of them. A complete long term solution may be PGO (profile-guided optimization) but it isn't available at this point. [1] https://lkml.org/lkml/2019/5/21/349 [2] https://www.spinics.net/lists/linux-block/msg40624.html [3] https://lore.kernel.org/linux-arm-kernel/066fc320-dc04-11a4-476e-b0d11f3b17e6@gmail.com/T/ [4] https://www.spinics.net/lists/netdev/msg816103.html [5] http://lists.openwrt.org/pipermail/openwrt-devel/2022-July/038989.html Signed-off-by: Rafał Miłecki <rafal@milecki.pl> (cherry picked from commit abc5b28db164dc2d807750cb2baae91e288c84a9)
-rw-r--r--config/Config-devel.in1
1 files changed, 1 insertions, 0 deletions
diff --git a/config/Config-devel.in b/config/Config-devel.in
index a068f694e5..87f9157106 100644
--- a/config/Config-devel.in
+++ b/config/Config-devel.in
@@ -76,6 +76,7 @@ menuconfig DEVEL
config KERNEL_CFLAGS
string "Kernel extra CFLAGS" if DEVEL
+ default "-falign-functions=32" if TARGET_bcm53xx
default ""
config EXTERNAL_KERNEL_TREE