Re: [PATCH] KSM: Replace jhash2 with xxhash

[Andi Kleen <ak@linux.intel.com>]

Timofey Titovets <nefelim4ag@gmail.com> writes:

> xxhash much faster then jhash,
> ex. for x86_64 host:
> PAGE_SIZE: 4096, loop count: 1048576
> jhash2:   0xacbc7a5b            time: 1907 ms,  th:  2251.9 MiB/s
> xxhash32: 0x570da981            time: 739 ms,   th:  5809.4 MiB/s
> xxhash64: 0xa1fa032ab85bbb62    time: 371 ms,   th: 11556.6 MiB/s
>
> xxhash64 on x86_32 work with ~ same speed as jhash2.
> xxhash32 on x86_32 work with ~ same speed as for x86_64

Which CPU is that?

>
> So replace jhash with xxhash,
> and use fastest version for current target ARCH.

Can you do some macro-benchmarking too? Something that uses
KSM and show how the performance changes.

You could manually increase the scan rate to make it easier
to see.

> @@ -51,6 +52,12 @@
>  #define DO_NUMA(x)	do { } while (0)
>  #endif
>  
> +#if BITS_PER_LONG == 64
> +typedef	u64	xxhash;
> +#else
> +typedef	u32	xxhash;
> +#endif

This should be in xxhash.h ? 

xxhash_t would seem to be a better name.

> -	u32 checksum;
> +	xxhash checksum;
>  	void *addr = kmap_atomic(page);
> -	checksum = jhash2(addr, PAGE_SIZE / 4, 17);
> +#if BITS_PER_LONG == 64
> +	checksum = xxh64(addr, PAGE_SIZE, 0);
> +#else
> +	checksum = xxh32(addr, PAGE_SIZE, 0);
> +#endif

This should also be generic in xxhash.h



-Andi

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