From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH v4 tip 3/7] tracing: allow BPF programs to call ktime_get_ns() Date: Sat, 28 Feb 2015 11:20:43 +0100 Message-ID: <20150228102043.GX5029@twins.programming.kicks-ass.net> References: <1425082135-11967-1-git-send-email-ast@plumgrid.com> <1425082135-11967-4-git-send-email-ast@plumgrid.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1425082135-11967-4-git-send-email-ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Alexei Starovoitov Cc: Ingo Molnar , Steven Rostedt , Namhyung Kim , Arnaldo Carvalho de Melo , Jiri Olsa , Masami Hiramatsu , "David S. Miller" , Daniel Borkmann , linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-api@vger.kernel.org On Fri, Feb 27, 2015 at 04:08:51PM -0800, Alexei Starovoitov wrote: > bpf_ktime_get_ns() is used by programs to compue time delta between events > or as a timestamp > > Signed-off-by: Alexei Starovoitov > --- > include/uapi/linux/bpf.h | 1 + > kernel/trace/bpf_trace.c | 10 ++++++++++ > 2 files changed, 11 insertions(+) > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > index 4486d36d2e9e..101e509d1001 100644 > --- a/include/uapi/linux/bpf.h > +++ b/include/uapi/linux/bpf.h > @@ -165,6 +165,7 @@ enum bpf_func_id { > BPF_FUNC_map_update_elem, /* int map_update_elem(&map, &key, &value, flags) */ > BPF_FUNC_map_delete_elem, /* int map_delete_elem(&map, &key) */ > BPF_FUNC_probe_read, /* int bpf_probe_read(void *dst, int size, void *src) */ > + BPF_FUNC_ktime_get_ns, /* u64 bpf_ktime_get_ns(void) */ > __BPF_FUNC_MAX_ID, > }; > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index bcce9b238dad..64b918488607 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -36,6 +36,11 @@ static u64 bpf_probe_read(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5) > return probe_kernel_read(dst, unsafe_ptr, size); > } > > +static u64 bpf_ktime_get_ns(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5) > +{ > + return ktime_get_ns(); > +} Please use ktime_get_mono_fast_ns() instead. If you ever want to allow running BPF stuff from general tracepoints and the like you need to be NMI safe.