Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1292796

Re: [PATCH 5/6] bpf: hash: avoid to call kmalloc() in eBPF prog

Show all headers | View raw

On Wed, Dec 16, 2015 at 7:10 AM, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
> On Tue, Dec 15, 2015 at 07:21:03PM +0800, Ming Lei wrote:
>> kmalloc() is often a bit time-consuming, also
>> one atomic counter has to be used to track the total
>> allocated elements, which is also not good.
>>
>> This patch pre-allocates element pool in htab_map_alloc(),
>> then use percpu_ida to allocate one slot from the pool,
>> then the runtime allocation/freeing cost can be decreased.
>>
>> From my test, at least 10% fio throughput is improved in block
>> I/O test when tools/biolatency of bcc(iovisor) is running.
>>
>> Signed-off-by: Ming Lei <tom.leiming@gmail.com>
>
> Looks very intersting as well.
> Approach looks good.
> If you can make a common allocation helper for this map and
> for blk-mq would be even better.

OK, I will see if it is doable.

>
>> -     htab->elem_size = sizeof(struct htab_elem) +
>> -                       round_up(htab->map.key_size, 8) +
>> -                       htab->map.value_size;
>> +     htab->elem_size = round_up(sizeof(struct htab_elem) +
>> +                                round_up(htab->map.key_size, 8) +
>> +                                htab->map.value_size,
>> +                                cache_line_size());
>
> this rounding to cache line is great for performance, but it's extra
> memory upfront which may not be needed. The per-allocation is a classic
> performance vs memory trade-off. In other cases it may hurt.

The current kmalloc allocation for 'struct htab_elem' is still cache line
aligned, that is one reason why I choose to do it, but we can change
it too.

> So could you change the patch to do pre-allocation only when
> requested by user space via extra flag for hash map or via
> new BPF_MAP_TYPE_HASH_PREALLOC type? Not sure yet whether flag or
> new type is better. I guess implementation will dictate.

Looks a better idea, then we can let user make the choice.

>
> PS
> Glad that you found iovisor/tools/biolatency useful.
> It's indeed pretty helpful to analyze real-time block io latency.

This tool is great and I have played it for a while, :-)



Thanks,
Ming Lei
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 0/6] bpf: hash: optimization Ming Lei <tom.leiming@gmail.com> - 2015-12-15 12:30 +0100
  [PATCH 6/6] bpf: hash: reorganize 'struct htab_elem' Ming Lei <tom.leiming@gmail.com> - 2015-12-15 12:30 +0100
  [PATCH 5/6] bpf: hash: avoid to call kmalloc() in eBPF prog Ming Lei <tom.leiming@gmail.com> - 2015-12-15 12:30 +0100
    Re: [PATCH 5/6] bpf: hash: avoid to call kmalloc() in eBPF prog Alexei Starovoitov <alexei.starovoitov@gmail.com> - 2015-12-16 00:20 +0100
      Re: [PATCH 5/6] bpf: hash: avoid to call kmalloc() in eBPF prog Daniel Borkmann <daniel@iogearbox.net> - 2015-12-16 00:50 +0100
      Re: [PATCH 5/6] bpf: hash: avoid to call kmalloc() in eBPF prog Ming Lei <tom.leiming@gmail.com> - 2015-12-16 08:20 +0100
    Re: [PATCH 5/6] bpf: hash: avoid to call kmalloc() in eBPF prog Daniel Borkmann <daniel@iogearbox.net> - 2015-12-16 00:30 +0100
    Re: [PATCH 5/6] bpf: hash: avoid to call kmalloc() in eBPF prog Daniel Borkmann <daniel@iogearbox.net> - 2015-12-16 00:40 +0100
      Re: [PATCH 5/6] bpf: hash: avoid to call kmalloc() in eBPF prog Daniel Borkmann <daniel@iogearbox.net> - 2015-12-16 01:20 +0100
  [PATCH 2/6] hlist: prepare for supporting bit spinlock Ming Lei <tom.leiming@gmail.com> - 2015-12-15 12:30 +0100
  [PATCH 1/6] bpf: hash: use atomic count Ming Lei <tom.leiming@gmail.com> - 2015-12-15 12:30 +0100
  [PATCH 3/6] bpf: hash: move select_bucket() out of htab's spinlock Ming Lei <tom.leiming@gmail.com> - 2015-12-15 12:30 +0100

csiph-web