netdev - Re: [PATCH] tools/runqslower: use _

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Date:   Tue, 6 Jul 2021 15:04:48 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     SanjayKumar J <vjsanjay@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH] tools/runqslower: use __state instead of state

On Tue, Jul 6, 2021 at 11:26 AM Yonghong Song <yhs@...com> wrote:
>
>
>
> On 7/6/21 10:44 AM, SanjayKumar J wrote:
> >       task->state is renamed to task->__state in task_struct
>
> Could you add a reference to
>    2f064a59a11f ("sched: Change task_struct::state")
> which added this change?
>
> I think this should go to bpf tree as the change is in linus tree now.
> Could you annotate the tag as "[PATCH bpf]" ("[PATCH bpf v2]")?
>
> Please align comments to the left without margins.
>
> >
> >       Signed-off-by: SanjayKumar J <vjsanjay@...il.com>
>
> This Singed-off-by is not needed.
>
> You can add my Ack in the next revision:
> Acked-by: Yonghong Song <yhs@...com>
>
> >
> > Signed-off-by: SanjayKumar J <vjsanjay@...il.com>
> > ---
> >   tools/bpf/runqslower/runqslower.bpf.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/bpf/runqslower/runqslower.bpf.c b/tools/bpf/runqslower/runqslower.bpf.c
> > index 645530ca7e98..ab9353f2fd46 100644
> > --- a/tools/bpf/runqslower/runqslower.bpf.c
> > +++ b/tools/bpf/runqslower/runqslower.bpf.c
> > @@ -74,7 +74,7 @@ int handle__sched_switch(u64 *ctx)
> >       u32 pid;
> >
> >       /* ivcsw: treat like an enqueue event and store timestamp */
> > -     if (prev->state == TASK_RUNNING)
> > +     if (prev->__state == TASK_RUNNING)
>
> Currently, runqslower.bpf.c uses vmlinux.h.
> I am thinking to use bpf_core_field_exists(), but we need to
> single out task_struct structure from vmlinux.h
> with both state and __state fields, we could make it work
> by *changes* like
>
> #define task_struct task_struct_orig
> #include "vmlinux.h"
> #undef task_struct
>
> struct task_struct {
>     ... state;
>     ... __state;
> ...
> };


no need for such surgery, recommended way is to use ___suffix to
declare incompatible struct definition:

struct task_struct___old {
    int state;
};

Then do casting in BPF code. We don't have to do it in kernel tree's
runqslower, but we'll definitely have to do that for libbpf-tools'
runqslower and runqlat.


>
> Considering tools/bpf/runqslower is tied with a particular
> kernel source, and vmlinux.h mostly derived from that
> kernel source, I feel the above change is not necessary.
>
> >               trace_enqueue(prev);
> >
> >       pid = next->pid;
> >