* [PATCH v2 bpf-next] bpf: optimize hashmap lookups when key_size is divisible by 4
@ 2023-04-01 20:06 Anton Protopopov
2023-04-01 22:10 ` Alexei Starovoitov
2023-04-01 22:20 ` patchwork-bot+netdevbpf
0 siblings, 2 replies; 4+ messages in thread
From: Anton Protopopov @ 2023-04-01 20:06 UTC (permalink / raw)
To: bpf, Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
Martin KaFai Lau, John Fastabend
Cc: Anton Protopopov
The BPF hashmap uses the jhash() hash function. There is an optimized version
of this hash function which may be used if hash size is a multiple of 4. Apply
this optimization to the hashmap in a similar way as it is done in the bloom
filter map.
On practice the optimization is only noticeable for smaller key sizes, which,
however, is sufficient for many applications. An example is listed in the
following table of measurements (a hashmap of 65536 elements was used):
--------------------------------------------------------------------
| key_size | fullness | lookups /sec | lookups (opt) /sec | gain |
--------------------------------------------------------------------
| 4 | 25% | 42.990M | 46.000M | 7.0% |
| 4 | 50% | 37.910M | 39.094M | 3.1% |
| 4 | 75% | 34.486M | 36.124M | 4.7% |
| 4 | 100% | 31.760M | 32.719M | 3.0% |
--------------------------------------------------------------------
| 8 | 25% | 43.855M | 49.626M | 13.2% |
| 8 | 50% | 38.328M | 42.152M | 10.0% |
| 8 | 75% | 34.483M | 38.088M | 10.5% |
| 8 | 100% | 31.306M | 34.686M | 10.8% |
--------------------------------------------------------------------
| 12 | 25% | 38.398M | 43.770M | 14.0% |
| 12 | 50% | 33.336M | 37.712M | 13.1% |
| 12 | 75% | 29.917M | 34.440M | 15.1% |
| 12 | 100% | 27.322M | 30.480M | 11.6% |
--------------------------------------------------------------------
| 16 | 25% | 41.491M | 41.921M | 1.0% |
| 16 | 50% | 36.206M | 36.474M | 0.7% |
| 16 | 75% | 32.529M | 33.027M | 1.5% |
| 16 | 100% | 29.581M | 30.325M | 2.5% |
--------------------------------------------------------------------
| 20 | 25% | 34.240M | 36.787M | 7.4% |
| 20 | 50% | 30.328M | 32.663M | 7.7% |
| 20 | 75% | 27.536M | 29.354M | 6.6% |
| 20 | 100% | 24.847M | 26.505M | 6.7% |
--------------------------------------------------------------------
| 24 | 25% | 36.329M | 40.608M | 11.8% |
| 24 | 50% | 31.444M | 35.059M | 11.5% |
| 24 | 75% | 28.426M | 31.452M | 10.6% |
| 24 | 100% | 26.278M | 28.741M | 9.4% |
--------------------------------------------------------------------
| 28 | 25% | 31.540M | 31.944M | 1.3% |
| 28 | 50% | 27.739M | 28.063M | 1.2% |
| 28 | 75% | 24.993M | 25.814M | 3.3% |
| 28 | 100% | 23.513M | 23.500M | -0.1% |
--------------------------------------------------------------------
| 32 | 25% | 32.116M | 33.953M | 5.7% |
| 32 | 50% | 28.879M | 29.859M | 3.4% |
| 32 | 75% | 26.227M | 26.948M | 2.7% |
| 32 | 100% | 23.829M | 24.613M | 3.3% |
--------------------------------------------------------------------
| 64 | 25% | 22.535M | 22.554M | 0.1% |
| 64 | 50% | 20.471M | 20.675M | 1.0% |
| 64 | 75% | 19.077M | 19.146M | 0.4% |
| 64 | 100% | 17.710M | 18.131M | 2.4% |
--------------------------------------------------------------------
The following script was used to gather the results (SMT & frequency off):
cd tools/testing/selftests/bpf
for key_size in 4 8 12 16 20 24 28 32 64; do
for nr_entries in `seq 16384 16384 65536`; do
fullness=$(printf '%3s' $((nr_entries*100/65536)))
echo -n "key_size=$key_size: $fullness% full: "
sudo ./bench -d2 -a bpf-hashmap-lookup --key_size=$key_size --nr_entries=$nr_entries --max_entries=65536 --nr_loops=2000000 --map_flags=0x40 | grep cpu
done
echo
done
Signed-off-by: Anton Protopopov <aspsk@isovalent.com>
---
v1->v2:
- simplify/optimize code by just testing the (key_len%4 == 0) in hot path (Alexei)
kernel/bpf/hashtab.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 96b645bba3a4..00c253b84bf5 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -607,6 +607,8 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
static inline u32 htab_map_hash(const void *key, u32 key_len, u32 hashrnd)
{
+ if (likely(key_len % 4 == 0))
+ return jhash2(key, key_len / 4, hashrnd);
return jhash(key, key_len, hashrnd);
}
--
2.34.1
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH v2 bpf-next] bpf: optimize hashmap lookups when key_size is divisible by 4
2023-04-01 20:06 [PATCH v2 bpf-next] bpf: optimize hashmap lookups when key_size is divisible by 4 Anton Protopopov
@ 2023-04-01 22:10 ` Alexei Starovoitov
2023-04-02 11:45 ` Anton Protopopov
2023-04-01 22:20 ` patchwork-bot+netdevbpf
1 sibling, 1 reply; 4+ messages in thread
From: Alexei Starovoitov @ 2023-04-01 22:10 UTC (permalink / raw)
To: Anton Protopopov
Cc: bpf, Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
Martin KaFai Lau, John Fastabend
On Sat, Apr 1, 2023 at 1:05 PM Anton Protopopov <aspsk@isovalent.com> wrote:
>
> The BPF hashmap uses the jhash() hash function. There is an optimized version
> of this hash function which may be used if hash size is a multiple of 4. Apply
> this optimization to the hashmap in a similar way as it is done in the bloom
> filter map.
>
> On practice the optimization is only noticeable for smaller key sizes, which,
> however, is sufficient for many applications. An example is listed in the
> following table of measurements (a hashmap of 65536 elements was used):
>
> --------------------------------------------------------------------
> | key_size | fullness | lookups /sec | lookups (opt) /sec | gain |
> --------------------------------------------------------------------
> | 4 | 25% | 42.990M | 46.000M | 7.0% |
> | 4 | 50% | 37.910M | 39.094M | 3.1% |
> | 4 | 75% | 34.486M | 36.124M | 4.7% |
> | 4 | 100% | 31.760M | 32.719M | 3.0% |
> --------------------------------------------------------------------
> | 8 | 25% | 43.855M | 49.626M | 13.2% |
> | 8 | 50% | 38.328M | 42.152M | 10.0% |
> | 8 | 75% | 34.483M | 38.088M | 10.5% |
> | 8 | 100% | 31.306M | 34.686M | 10.8% |
> --------------------------------------------------------------------
> | 12 | 25% | 38.398M | 43.770M | 14.0% |
> | 12 | 50% | 33.336M | 37.712M | 13.1% |
> | 12 | 75% | 29.917M | 34.440M | 15.1% |
> | 12 | 100% | 27.322M | 30.480M | 11.6% |
> --------------------------------------------------------------------
> | 16 | 25% | 41.491M | 41.921M | 1.0% |
> | 16 | 50% | 36.206M | 36.474M | 0.7% |
> | 16 | 75% | 32.529M | 33.027M | 1.5% |
> | 16 | 100% | 29.581M | 30.325M | 2.5% |
> --------------------------------------------------------------------
> | 20 | 25% | 34.240M | 36.787M | 7.4% |
> | 20 | 50% | 30.328M | 32.663M | 7.7% |
> | 20 | 75% | 27.536M | 29.354M | 6.6% |
> | 20 | 100% | 24.847M | 26.505M | 6.7% |
> --------------------------------------------------------------------
> | 24 | 25% | 36.329M | 40.608M | 11.8% |
> | 24 | 50% | 31.444M | 35.059M | 11.5% |
> | 24 | 75% | 28.426M | 31.452M | 10.6% |
> | 24 | 100% | 26.278M | 28.741M | 9.4% |
> --------------------------------------------------------------------
> | 28 | 25% | 31.540M | 31.944M | 1.3% |
> | 28 | 50% | 27.739M | 28.063M | 1.2% |
> | 28 | 75% | 24.993M | 25.814M | 3.3% |
> | 28 | 100% | 23.513M | 23.500M | -0.1% |
> --------------------------------------------------------------------
> | 32 | 25% | 32.116M | 33.953M | 5.7% |
> | 32 | 50% | 28.879M | 29.859M | 3.4% |
> | 32 | 75% | 26.227M | 26.948M | 2.7% |
> | 32 | 100% | 23.829M | 24.613M | 3.3% |
> --------------------------------------------------------------------
> | 64 | 25% | 22.535M | 22.554M | 0.1% |
> | 64 | 50% | 20.471M | 20.675M | 1.0% |
> | 64 | 75% | 19.077M | 19.146M | 0.4% |
> | 64 | 100% | 17.710M | 18.131M | 2.4% |
> --------------------------------------------------------------------
>
> The following script was used to gather the results (SMT & frequency off):
>
> cd tools/testing/selftests/bpf
> for key_size in 4 8 12 16 20 24 28 32 64; do
> for nr_entries in `seq 16384 16384 65536`; do
> fullness=$(printf '%3s' $((nr_entries*100/65536)))
> echo -n "key_size=$key_size: $fullness% full: "
> sudo ./bench -d2 -a bpf-hashmap-lookup --key_size=$key_size --nr_entries=$nr_entries --max_entries=65536 --nr_loops=2000000 --map_flags=0x40 | grep cpu
> done
> echo
> done
>
> Signed-off-by: Anton Protopopov <aspsk@isovalent.com>
> ---
>
> v1->v2:
> - simplify/optimize code by just testing the (key_len%4 == 0) in hot path (Alexei)
>
> kernel/bpf/hashtab.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
> index 96b645bba3a4..00c253b84bf5 100644
> --- a/kernel/bpf/hashtab.c
> +++ b/kernel/bpf/hashtab.c
> @@ -607,6 +607,8 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
>
> static inline u32 htab_map_hash(const void *key, u32 key_len, u32 hashrnd)
> {
> + if (likely(key_len % 4 == 0))
> + return jhash2(key, key_len / 4, hashrnd);
> return jhash(key, key_len, hashrnd);
> }
This looks much cleaner than v1. Applied.
Do you mind doing similar patch for bloomfilter?
(removing aligned_u32_count variable)
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH v2 bpf-next] bpf: optimize hashmap lookups when key_size is divisible by 4
2023-04-01 22:10 ` Alexei Starovoitov
@ 2023-04-02 11:45 ` Anton Protopopov
0 siblings, 0 replies; 4+ messages in thread
From: Anton Protopopov @ 2023-04-02 11:45 UTC (permalink / raw)
To: Alexei Starovoitov
Cc: bpf, Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
Martin KaFai Lau, John Fastabend
On Sat, Apr 01, 2023 at 03:10:46PM -0700, Alexei Starovoitov wrote:
> On Sat, Apr 1, 2023 at 1:05 PM Anton Protopopov <aspsk@isovalent.com> wrote:
> >
> > [...]
> >
> > static inline u32 htab_map_hash(const void *key, u32 key_len, u32 hashrnd)
> > {
> > + if (likely(key_len % 4 == 0))
> > + return jhash2(key, key_len / 4, hashrnd);
> > return jhash(key, key_len, hashrnd);
> > }
>
> This looks much cleaner than v1. Applied.
Thanks!
> Do you mind doing similar patch for bloomfilter?
> (removing aligned_u32_count variable)
Sure, done.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2 bpf-next] bpf: optimize hashmap lookups when key_size is divisible by 4
2023-04-01 20:06 [PATCH v2 bpf-next] bpf: optimize hashmap lookups when key_size is divisible by 4 Anton Protopopov
2023-04-01 22:10 ` Alexei Starovoitov
@ 2023-04-01 22:20 ` patchwork-bot+netdevbpf
1 sibling, 0 replies; 4+ messages in thread
From: patchwork-bot+netdevbpf @ 2023-04-01 22:20 UTC (permalink / raw)
To: Anton Protopopov; +Cc: bpf, ast, daniel, andrii, martin.lau, john.fastabend
Hello:
This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:
On Sat, 1 Apr 2023 20:06:02 +0000 you wrote:
> The BPF hashmap uses the jhash() hash function. There is an optimized version
> of this hash function which may be used if hash size is a multiple of 4. Apply
> this optimization to the hashmap in a similar way as it is done in the bloom
> filter map.
>
> On practice the optimization is only noticeable for smaller key sizes, which,
> however, is sufficient for many applications. An example is listed in the
> following table of measurements (a hashmap of 65536 elements was used):
>
> [...]
Here is the summary with links:
- [v2,bpf-next] bpf: optimize hashmap lookups when key_size is divisible by 4
https://git.kernel.org/bpf/bpf-next/c/5b85575ad428
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html
^ permalink raw reply [flat|nested] 4+ messages in thread
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2023-04-01 20:06 [PATCH v2 bpf-next] bpf: optimize hashmap lookups when key_size is divisible by 4 Anton Protopopov
2023-04-01 22:10 ` Alexei Starovoitov
2023-04-02 11:45 ` Anton Protopopov
2023-04-01 22:20 ` patchwork-bot+netdevbpf
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