Re: [PATCH bpf-next 0/6] bpf: add BPF_MAP_DUMP command to dump more than one entry per call
From: Brian Vazquez
Date: Wed Jul 24 2019 - 18:16:07 EST
On Wed, Jul 24, 2019 at 12:20 PM Song Liu <liu.song.a23@xxxxxxxxx> wrote:
> On Wed, Jul 24, 2019 at 10:09 AM Brian Vazquez <brianvv@xxxxxxxxxx> wrote:
> > This introduces a new command to retrieve multiple number of entries
> > from a bpf map.
> > This new command can be executed from the existing BPF syscall as
> > follows:
> > err = bpf(BPF_MAP_DUMP, union bpf_attr *attr, u32 size)
> > using attr->dump.map_fd, attr->dump.prev_key, attr->dump.buf,
> > attr->dump.buf_len
> > returns zero or negative error, and populates buf and buf_len on
> > succees
> > This implementation is wrapping the existing bpf methods:
> > map_get_next_key and map_lookup_elem
> > Note that this implementation can be extended later to do dump and
> > delete by extending map_lookup_and_delete_elem (currently it only works
> > for bpf queue/stack maps) and either use a new flag in map_dump or a new
> > command map_dump_and_delete.
> > Results show that even with a 1-elem_size buffer, it runs ~40 faster
> Why is the new command 40% faster with 1-elem_size buffer?
The test is using a really simple map structure: uint64_t key,val.
Which makes the lookup_elem logic faster since it doesn't spend too
much time copying the value. My conclusion with the 40% was that this
new implementation only needs 1 syscall per elem compare to the 2
syscalls that we needed with previous implementation so in this
particular case the number of ops that we are doing is almost halved.
I did one experiment increasing the value_size (448*64B) and it was
only 14% faster with 1-elem_size buffer.
> > than the current implementation, improvements of ~85% are reported when
> > the buffer size is increased, although, after the buffer size is around
> > 5% of the total number of entries there's no huge difference in
> > increasing it.
> > Tested:
> > Tried different size buffers to handle case where the bulk is bigger, or
> > the elements to retrieve are less than the existing ones, all runs read
> > a map of 100K entries. Below are the results(in ns) from the different
> > runs:
> > buf_len_1: 69038725 entry-by-entry: 112384424 improvement
> > 38.569134
> > buf_len_2: 40897447 entry-by-entry: 111030546 improvement
> > 63.165590
> > buf_len_230: 13652714 entry-by-entry: 111694058 improvement
> > 87.776687
> > buf_len_5000: 13576271 entry-by-entry: 111101169 improvement
> > 87.780263
> > buf_len_73000: 14694343 entry-by-entry: 111740162 improvement
> > 86.849542
> > buf_len_100000: 13745969 entry-by-entry: 114151991 improvement
> > 87.958187
> > buf_len_234567: 14329834 entry-by-entry: 114427589 improvement
> > 87.476941
> It took me a while to figure out the meaning of 87.476941. It is probably
> a good idea to say 87.5% instead.
right, will change it in next version.