Re: [PATCH bpf-next v2 0/5] execmem_alloc for BPF programs

[Mike Rapoport <rppt@kernel.org>]

On Wed, Nov 16, 2022 at 02:33:37PM -0800, Luis Chamberlain wrote:
> On Tue, Nov 15, 2022 at 02:48:05PM -0800, Song Liu wrote:
> > On Tue, Nov 15, 2022 at 1:09 PM Luis Chamberlain <mcgrof@kernel.org> wrote:
> > >
> > > On Mon, Nov 14, 2022 at 05:30:39PM -0800, Song Liu wrote:
> > > > On Mon, Nov 7, 2022 at 2:41 PM Song Liu <song@kernel.org> wrote:
> > >
> > > > Currently, I have got the following action items for v3:
> > > > 1. Add unify API to allocate text memory to motivation;
> > > > 2. Update Documentation/x86/x86_64/mm.rst;
> > > > 3. Allow none PMD_SIZE allocation for powerpc.
> > >
> > > - I am really exausted of asking again for real performance tests,
> > >   you keep saying you can't and I keep saying you can, you are not
> > >   trying hard enough. Stop thinking about your internal benchmark which
> > >   you cannot publish. There should be enough crap out which you can use.
> > >
> > > - A new selftest or set of selftests which demonstrates gain in
> > >   performance
> > 
> > I didn't mean to not show the result with publically available. I just
> > thought the actual benchmark was better (and we do use that to
> > demonstrate the benefit of a lot of kernel improvement).
> > 
> > For something publically available, how about the following:
> > 
> > Run 100 instances of the following benchmark from bpf selftests:
> >   tools/testing/selftests/bpf/bench -w2 -d100 -a trig-kprobe
> > which loads 7 BPF programs, and triggers one of them.
> > 
> > Then use perf to monitor TLB related counters:
> >    perf stat -e iTLB-load-misses,itlb_misses.walk_completed_4k, \
> >         itlb_misses.walk_completed_2m_4m -a
> > 
> > The following results are from a qemu VM with 32 cores.
> > 
> > Before bpf_prog_pack:
> >   iTLB-load-misses: 350k/s
> >   itlb_misses.walk_completed_4k: 90k/s
> >   itlb_misses.walk_completed_2m_4m: 0.1/s
> > 
> > With bpf_prog_pack (current upstream):
> >   iTLB-load-misses: 220k/s
> >   itlb_misses.walk_completed_4k: 68k/s
> >   itlb_misses.walk_completed_2m_4m: 0.2/s
> > 
> > With execmem_alloc (with this set):
> >   iTLB-load-misses: 185k/s
> >   itlb_misses.walk_completed_4k: 58k/s
> >   itlb_misses.walk_completed_2m_4m: 1/s
> > 
> > Do these address your questions with this?
> 
> More in lines with what I was hoping for. Can something just do
> the parallelization for you in one shot? Can bench alone do it for you?
> Is there no interest to have soemthing which generically showcases
> multithreading / hammering a system with tons of eBPF JITs? It may
> prove useful.
> 
> And also, it begs the question, what if you had another iTLB generic
> benchmark or genearl memory pressure workload running *as* you run the
> above? I as, as it was my understanding that one of the issues was the
> long term slowdown caused by the directmap fragmentation without
> bpf_prog_pack, and so such an application should crawl to its knees
> over time, and there should be numbers you could show to prove that
> too, before and after.

I'd add to that that benchmarking iTLB performance on an idle system is not
very representative. TLB is a scarce resource, so it'd be interesting to
see this benchmark on a loaded system.
 
>   Luis

-- 
Sincerely yours,
Mike.