On Tue, Aug 27, 2024 at 8:55 PM Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
>
> On Tue, 13 Aug 2024 13:34:09 -0700
> Andrii Nakryiko <andrii@xxxxxxxxxx> wrote:
>
> > trace_uprobe->nhit counter is not incremented atomically, so its value
> > is questionable in when uprobe is hit on multiple CPUs simultaneously.
> >
> > Also, doing this shared counter increment across many CPUs causes heavy
> > cache line bouncing, limiting uprobe/uretprobe performance scaling with
> > number of CPUs.
> >
> > Solve both problems by making this a per-CPU counter.
> >
>
> Looks good to me. Let me pick it to linux-trace probes/for-next.
>
Thanks! I just checked linux-trace repo, doesn't seem like this was
applied yet, is that right? Or am I checking in the wrong place?
> Thank you,
>
>
> > Reviewed-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> > Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> > ---
> > kernel/trace/trace_uprobe.c | 24 +++++++++++++++++++++---
> > 1 file changed, 21 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> > index c98e3b3386ba..c3df411a2684 100644
> > --- a/kernel/trace/trace_uprobe.c
> > +++ b/kernel/trace/trace_uprobe.c
> > @@ -17,6 +17,7 @@
> > #include <linux/string.h>
> > #include <linux/rculist.h>
> > #include <linux/filter.h>
> > +#include <linux/percpu.h>
> >
> > #include "trace_dynevent.h"
> > #include "trace_probe.h"
> > @@ -62,7 +63,7 @@ struct trace_uprobe {
> > char *filename;
> > unsigned long offset;
> > unsigned long ref_ctr_offset;
> > - unsigned long nhit;
> > + unsigned long __percpu *nhits;
> > struct trace_probe tp;
> > };
> >
> > @@ -337,6 +338,12 @@ alloc_trace_uprobe(const char *group, const char *event, int nargs, bool is_ret)
> > if (!tu)
> > return ERR_PTR(-ENOMEM);
> >
> > + tu->nhits = alloc_percpu(unsigned long);
> > + if (!tu->nhits) {
> > + ret = -ENOMEM;
> > + goto error;
> > + }
> > +
> > ret = trace_probe_init(&tu->tp, event, group, true, nargs);
> > if (ret < 0)
> > goto error;
> > @@ -349,6 +356,7 @@ alloc_trace_uprobe(const char *group, const char *event, int nargs, bool is_ret)
> > return tu;
> >
> > error:
> > + free_percpu(tu->nhits);
> > kfree(tu);
> >
> > return ERR_PTR(ret);
> > @@ -362,6 +370,7 @@ static void free_trace_uprobe(struct trace_uprobe *tu)
> > path_put(&tu->path);
> > trace_probe_cleanup(&tu->tp);
> > kfree(tu->filename);
> > + free_percpu(tu->nhits);
> > kfree(tu);
> > }
> >
> > @@ -815,13 +824,21 @@ static int probes_profile_seq_show(struct seq_file *m, void *v)
> > {
> > struct dyn_event *ev = v;
> > struct trace_uprobe *tu;
> > + unsigned long nhits;
> > + int cpu;
> >
> > if (!is_trace_uprobe(ev))
> > return 0;
> >
> > tu = to_trace_uprobe(ev);
> > +
> > + nhits = 0;
> > + for_each_possible_cpu(cpu) {
> > + nhits += per_cpu(*tu->nhits, cpu);
> > + }
> > +
> > seq_printf(m, " %s %-44s %15lu\n", tu->filename,
> > - trace_probe_name(&tu->tp), tu->nhit);
> > + trace_probe_name(&tu->tp), nhits);
> > return 0;
> > }
> >
> > @@ -1512,7 +1529,8 @@ static int uprobe_dispatcher(struct uprobe_consumer *con, struct pt_regs *regs)
> > int ret = 0;
> >
> > tu = container_of(con, struct trace_uprobe, consumer);
> > - tu->nhit++;
> > +
> > + this_cpu_inc(*tu->nhits);
> >
> > udd.tu = tu;
> > udd.bp_addr = instruction_pointer(regs);
> > --
> > 2.43.5
> >
>
>
> --
> Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
>
