On 07/03, Y Song wrote:
> On Wed, Jul 3, 2019 at 1:51 PM Stanislav Fomichev <sdf@xxxxxxxxxx> wrote:
> >
> > Take the first x bytes of pt_regs for scalability tests, there is
> > no real reason we need x86 specific rax.
> >
> > Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> > ---
> > tools/testing/selftests/bpf/progs/loop1.c | 3 ++-
> > tools/testing/selftests/bpf/progs/loop2.c | 3 ++-
> > tools/testing/selftests/bpf/progs/loop3.c | 3 ++-
> > 3 files changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/testing/selftests/bpf/progs/loop1.c b/tools/testing/selftests/bpf/progs/loop1.c
> > index dea395af9ea9..d530c61d2517 100644
> > --- a/tools/testing/selftests/bpf/progs/loop1.c
> > +++ b/tools/testing/selftests/bpf/progs/loop1.c
> > @@ -14,11 +14,12 @@ SEC("raw_tracepoint/kfree_skb")
> > int nested_loops(volatile struct pt_regs* ctx)
> > {
> > int i, j, sum = 0, m;
> > + volatile int *any_reg = (volatile int *)ctx;
> >
> > for (j = 0; j < 300; j++)
> > for (i = 0; i < j; i++) {
> > if (j & 1)
> > - m = ctx->rax;
> > + m = *any_reg;
>
> I agree. ctx->rax here is only to generate some operations, which
> cannot be optimized away by the compiler. dereferencing a volatile
> pointee may just serve that purpose.
>
> Comparing the byte code generated with ctx->rax and *any_reg, they are
> slightly different. Using *any_reg is slighly worse, but this should
> be still okay for the test.
>
> > else
> > m = j;
> > sum += i * m;
> > diff --git a/tools/testing/selftests/bpf/progs/loop2.c b/tools/testing/selftests/bpf/progs/loop2.c
> > index 0637bd8e8bcf..91bb89d901e3 100644
> > --- a/tools/testing/selftests/bpf/progs/loop2.c
> > +++ b/tools/testing/selftests/bpf/progs/loop2.c
> > @@ -14,9 +14,10 @@ SEC("raw_tracepoint/consume_skb")
> > int while_true(volatile struct pt_regs* ctx)
> > {
> > int i = 0;
> > + volatile int *any_reg = (volatile int *)ctx;
> >
> > while (true) {
> > - if (ctx->rax & 1)
> > + if (*any_reg & 1)
> > i += 3;
> > else
> > i += 7;
> > diff --git a/tools/testing/selftests/bpf/progs/loop3.c b/tools/testing/selftests/bpf/progs/loop3.c
> > index 30a0f6cba080..3a7f12d7186c 100644
> > --- a/tools/testing/selftests/bpf/progs/loop3.c
> > +++ b/tools/testing/selftests/bpf/progs/loop3.c
> > @@ -14,9 +14,10 @@ SEC("raw_tracepoint/consume_skb")
> > int while_true(volatile struct pt_regs* ctx)
> > {
> > __u64 i = 0, sum = 0;
> > + volatile __u64 *any_reg = (volatile __u64 *)ctx;
> > do {
> > i++;
> > - sum += ctx->rax;
> > + sum += *any_reg;
> > } while (i < 0x100000000ULL);
> > return sum;
> > }
> > --
> > 2.22.0.410.gd8fdbe21b5-goog
>
> Ilya Leoshkevich (iii@xxxxxxxxxxxxx, cc'ed) has another patch set
> trying to solve this problem by introducing s360 arch register access
> macros. I guess for now that patch set is not needed any more?
Oh, I missed them. Do they fix the tests for other (non-s360) arches as
well? I was trying to fix the issue by not depending on any arch
specific stuff because the test really doesn't care :-)
