Re: [PATCH 1/3] net: bpf jit: ppc: optimize choose_load_func error path

Vladimir Murzin
2013-10-13T14:26:39Z

On Wed, Oct 09, 2013 at 12:50:32AM +0200, Jan Seiffert wrote:
> Vladimir Murzin schrieb:
> > Macro CHOOSE_LOAD_FUNC returns handler for "any offset" if checks for K
> > were not passed. At the same time handlers for "any offset" cases make
> > the same checks against r_addr at run-time, that will always lead to
> > bpf_error.
> >
>
> Hmmm, if i only would remember why i wrote it that way....
> I memory serves me right the idea was to always have a solid fall back, no
> matter what, to the generic load function which works more like the load_pointer
> from filter.c.
> This way the COOSE-macro may could have been used at more places, but that
> never played out.
>
> And since all i wanted was to get the negative indirect load fixed,
> optimizing the constant error case was not on my plate.
> That you can get your negative K filter JITed in the first place, even
> if the constant error case was slower than necessary, was good enough ;)
>
> The ARM JIT is broken till this date...

... and s390 too.

>
> You can have my
> I'm-OK-with-this: Jan Seiffert <kaffeemonster@googlemail.com>
>
> for all three patches, -ENOTIME for a full review ATM.
>

Thanks for feedback, Jan!

> > Run-time checks are still necessary for indirect load operations, but
> > error path for absolute and mesh loads are worth to optimize during bpf
> > compile time.
> >
> > Signed-off-by: Vladimir Murzin <murzin.v@gmail.com>
> >
> > Cc: Jan Seiffert <kaffeemonster@googlemail.com>
> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > Cc: Paul Mackerras <paulus@samba.org>
> > Cc: Daniel Borkmann <dborkman@redhat.com>
> > Cc: Matt Evans <matt@ozlabs.org>
> >
> > ---
> > arch/powerpc/net/bpf_jit_comp.c | 7 ++++++-
> > 1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> > index bf56e33..754320a 100644
> > --- a/arch/powerpc/net/bpf_jit_comp.c
> > +++ b/arch/powerpc/net/bpf_jit_comp.c
> > @@ -132,7 +132,7 @@ static void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
> > }
> >
> > #define CHOOSE_LOAD_FUNC(K, func) \
> > - ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : func) : func##_positive_offset)
> > + ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : NULL) : func##_positive_offset)
> >
> > /* Assemble the body code between the prologue & epilogue. */
> > static int bpf_jit_build_body(struct sk_filter *fp, u32 *image,
> > @@ -427,6 +427,11 @@ static int bpf_jit_build_body(struct sk_filter *fp, u32 *image,
> > case BPF_S_LD_B_ABS:
> > func = CHOOSE_LOAD_FUNC(K, sk_load_byte);
> > common_load:
> > + if (!func) {
> > + PPC_LI(r_ret, 0);
> > + PPC_JMP(exit_addr);
> > + break;
> > + }
> > /* Load from [K]. */
> > ctx->seen |= SEEN_DATAREF;
> > PPC_LI64(r_scratch1, func);
> >
>
>
> --
> An UDP packet walks into a