Re: [PATCH bpf-next v4 0/3] bpf, arm64: use BPF prog pack allocator in BPF JIT

[Florent Revest]

On Thu, Aug 3, 2023 at 6:16 PM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> On Thu, Aug 3, 2023 at 4:13 AM Mark Rutland <mark.rutland@xxxxxxx> wrote:
> >
> > Hi Alexei,
> >
> > On Wed, Aug 02, 2023 at 02:02:39PM -0700, Alexei Starovoitov wrote:
> > > Mark, Catalin, Florent, KP,

Maybe you've missed my Acked-by for the series Alexei ?
https://lore.kernel.org/all/CABRcYmLAzhG=o2wcBNBtFP34Aj3+eYsEMtMREDT7SqNzBc9-qw@xxxxxxxxxxxxxx/

> > > This patch set was submitted on June 26 !
> >
> > I appreciate this was sent a while ago, but I have been stuck on some urgent
> > bug-fixing for the last few weeks, and my review bandwidth is therfore very
> > limited.
> >
> > Given Puranjay had previously told me he was doing this as a side project for
> > fun, and given no-one had told me this was urgent, I assumed that this wasn't a
> > major blocker and could wait.
> >
> > I should have sent a holding reply to that effect; sorry.
> >
> > The series addresses my original concern. However, in looking at it I think
> > there may me a wider potential isssue w.r.t. the way instruction memory gets
> > reused, because as writtten today the architecture doesn't seem to have a
> > guarantee on when instruction fetches are completed and therefore when it's
> > safe to modify instruction memory. Usually we're saved by TLB maintenance,
> > which this series avoids by design.

But I must say that this sits firmly outside of my knowledge of the
arm architectural details and I would totally miss this sort of nuance
so this is best handled by arm64 maintainers :)

> > I unfortunately haven't had the time to dig into that, poke our architects,
> > etc.
> >
> > So how urgent is this?
>
> The performance wins are substantial.
> We'd like to realize them sooner than later.

I've worked with Mark before, I know for a fact that he is dragged in
all directions. Until we figure out a way to clone him we should try
to not burn him out too often... :)