Re: [PATCH] Revert "arm64: Increase the max granular size"

[Chalamarla, Tirumalesh]

On 3/16/16, 2:32 AM, "linux-arm-kernel on behalf of Ganesh Mahendran" <linux-arm-kernel-bounces@xxxxxxxxxxxxxxxxxxx on behalf of opensource.ganesh@xxxxxxxxx> wrote:

>Reverts commit 97303480753e ("arm64: Increase the max granular size").
>
>The commit 97303480753e ("arm64: Increase the max granular size") will
>degrade system performente in some cpus.
>
>We test wifi network throughput with iperf on Qualcomm msm8996 CPU:
>----------------
>run on host:
>  # iperf -s
>run on device:
>  # iperf -c <device-ip-addr> -t 100 -i 1
>----------------
>
>Test result:
>----------------
>with commit 97303480753e ("arm64: Increase the max granular size"):
>    172MBits/sec
>
>without commit 97303480753e ("arm64: Increase the max granular size"):
>    230MBits/sec
>----------------
>
>Some module like slab/net will use the L1_CACHE_SHIFT, so if we do not
>set the parameter correctly, it may affect the system performance.
>
>So revert the commit.

Is there any explanation why is this so? May be there is an alternative to this, apart from reverting the commit.

Until now it seems L1_CACHE_SHIFT is the max of supported chips. But now we are making it 64byte, is there any reason why not 32. 

Thanks,
Tirumalesh. 
>
>Cc: stable@xxxxxxxxxxxxxxx
>Signed-off-by: Ganesh Mahendran <opensource.ganesh@xxxxxxxxx>
>---
> arch/arm64/include/asm/cache.h |    2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h
>index 5082b30..bde4499 100644
>--- a/arch/arm64/include/asm/cache.h
>+++ b/arch/arm64/include/asm/cache.h
>@@ -18,7 +18,7 @@
> 
> #include <asm/cachetype.h>
> 
>-#define L1_CACHE_SHIFT		7
>+#define L1_CACHE_SHIFT		6
> #define L1_CACHE_BYTES		(1 << L1_CACHE_SHIFT)
> 
> /*
>-- 
>1.7.9.5
>
>
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