Use prctl to enable/ disable perf for lower overhead (#38)

prctl will enable or disable all benches, so you need to close them after you're done with them otherwise you'll quickly have too many benches and you won't get any results out of your new ones (not sure if the old ones will give results).

Co-authored-by: Zentrik <[email protected]>

Author: Zentrik

src/LinuxPerf.jl

@@ -325,6 +325,20 @@ function Base.show(io::IO, g::EventGroup)
     print(io, "\t", g.event_types[end], ")")
 end
 
+const SYS_prctl = Clong(157)
+const PR_TASK_PERF_EVENTS_DISABLE = Cint(31)
+const PR_TASK_PERF_EVENTS_ENABLE = Cint(32)
+
+# syscall is lower overhead than calling libc's prctl
+function enable_all!()
+    res = ccall(:syscall, Cint, (Clong, Clong...), SYS_prctl, PR_TASK_PERF_EVENTS_ENABLE)
+    Base.systemerror(:prctl, res < 0)
+end
+function disable_all!()
+    res = ccall(:syscall, Cint, (Clong, Clong...), SYS_prctl, PR_TASK_PERF_EVENTS_DISABLE)
+    Base.systemerror(:prctl, res < 0)
+end
+
 const PERF_EVENT_IOC_ENABLE =  UInt64(0x2400)
 const PERF_EVENT_IOC_DISABLE = UInt64(0x2401)
 const PERF_EVENT_IOC_RESET =   UInt64(0x2403)
@@ -1068,9 +1082,9 @@ macro pstats(args...)
             @debug dump_groups(groups)
             bench = make_bench_threaded(groups, threads = $(opts.threads))
             try
-                enable!(bench)
+                enable_all!()
                 val = $(esc(expr))
-                disable!(bench)
+                disable_all!()
                 # trick the compiler not to eliminate the code
                 stats = rand() < 0 ? val : Stats(bench)
                 return stats::Stats

test/runtests.jl

@@ -1,7 +1,7 @@
 using LinuxPerf
 using Test
 
-using LinuxPerf: make_bench, enable!, disable!, reset!, reasonable_defaults, counters, EventType, EventTypeExt, parse_groups
+using LinuxPerf: make_bench, enable!, disable!, reset!, reasonable_defaults, counters, EventType, EventTypeExt, parse_groups, enable_all!, disable_all!
 
 @testset "LinuxPerf" begin
 
@@ -21,7 +21,29 @@ using LinuxPerf: make_bench, enable!, disable!, reset!, reasonable_defaults, cou
         end
         g(zeros(10000))
 
-        counters(bench)
+        results = counters(bench)
+        close(bench)
+
+        true  # Succeeded without any exceptions...
+    end
+
+    @test begin
+        bench = make_bench(reasonable_defaults);
+        @noinline function g(a)
+            enable_all!()
+            c = 0
+            for x in a
+                if x > 0
+                    c += 1
+                end
+            end
+            disable_all!()
+            c
+        end
+        g(zeros(10000))
+
+        results = counters(bench)
+        close(bench)
 
         true  # Succeeded without any exceptions...
     end