From: Igor Munkin via Tarantool-discussions <tarantool-discussions@dev.tarantool.org> To: Sergey Kaplun <skaplun@tarantool.org> Cc: tarantool-discussions@dev.tarantool.org Subject: Re: [Tarantool-discussions] [RFC luajit v3] rfc: describe a LuaJIT memory profiler Date: Fri, 15 Jan 2021 16:14:24 +0300 [thread overview] Message-ID: <20210115131424.GA5460@tarantool.org> (raw) In-Reply-To: <20201225113431.9538-1-skaplun@tarantool.org> Sergey, Thanks for the changes. There is a bit of nitpicking below and I believe we'll push the next version doc to the trunk. On 25.12.20, Sergey Kaplun wrote: > Part of #5442 > --- > > RFC on branch: https://github.com/tarantool/tarantool/blob/skaplun/gh-5442-luajit-memory-profiler/doc/rfc/5442-luajit-memory-profiler.md > > Changes in v3: > * More comments in example. > * More verbose benchmark information. > * Grammar and spelling fixes. > > Changes in v2: > * Removed C API, Tarantool integration and description of additional > features -- they will be added in another RFC if necessary. > * Removed checking profile is running from the public API. > * Added benchmarks and more meaningful example. > * Grammar fixes. > > doc/rfc/5442-luajit-memory-profiler.md | 314 +++++++++++++++++++++++++ > 1 file changed, 314 insertions(+) > create mode 100644 doc/rfc/5442-luajit-memory-profiler.md > > diff --git a/doc/rfc/5442-luajit-memory-profiler.md b/doc/rfc/5442-luajit-memory-profiler.md > new file mode 100644 > index 000000000..85a61462a > --- /dev/null > +++ b/doc/rfc/5442-luajit-memory-profiler.md > @@ -0,0 +1,314 @@ <snipped> > +### Prerequisites > + > +This section describes additional changes in LuaJIT required for the feature > +implementation. This version of LuaJIT memory profiler does not support verbose > +reporting allocations from traces. All allocation from traces are reported as Typo: s/reporting allocations from/reporting for allocations made on/. > +internal. But trace code semantics should be totally the same as for the Lua > +interpreter (excluding sink optimizations). Also all deallocations reported as Typo: s/deallocations reported/deallocation are reported/. > +internal too. > + > +There are two different representations of functions in LuaJIT: the function's > +prototype (`GCproto`) and the function object so called closure (`GCfunc`). > +The closures are represented as `GCfuncL` and `GCfuncC` for Lua and C closures > +correspondingly. Also LuaJIT has a special function's type aka Fast Function. Typo: s/correspondingly/respectively/. > +It is used for LuaJIT builtins. It's better to not split this sentence. Consider the rewording: | Besides LuaJIT has a special function type a.k.a. Fast Function that | is used for LuaJIT builtins. > + <snipped> > +Usually developers are not interested in information about allocations inside > +builtins. So if fast function was called from a Lua function all > +allocations are attributed to this Lua function. Otherwise attribute this event > +to a C function. I propose the following rewording: | Lua developers can do nothing with allocations made inside the | builtins except reducing its usage. So if fast function is called from | a Lua function all allocations made in its scope are attributed to this | Lua function (i.e. the builtin caller). Otherwise this event is | attributed to a C function. > + <snipped> > +If one run the chunk above the profiler reports approximately the following Typo: s/run/runs/. > +(see legend [here](#reading-and-displaying-saved-data)): <snipped> > +So we need to know a type of function being executed by the virtual machine > +(VM). Currently VM state identifies C function execution only, so Fast and Lua > +functions states will be added. Typo: s/will be/are/. > + > +To determine currently allocating coroutine (that may not be equal to currently > +executed one) a new field called `mem_L` is added to `global_State` structure > +to keep the coroutine address. This field is set at each reallocation to Typo: /at each reallocation to/on each reallocation to the/. > +corresponding `L` with which it was called. Typo: s/it was/it is/. > + <snipped> > +When the profiling is stopped the `fclose()` is called. If it is impossible to Typo: s/the `fclose()`/`fclose()`/. > +open a file for writing or profiler fails to start, returns `nil` on failure Typo: s/returns `nil`/`nil` is returned/. > +(plus an error message as a second result and a system-dependent error code as > +a third result). Otherwise returns some true value. It would be nice to mention that the function contract is similar to other standart io.* interfaces. I glanced the source code: it's not "some" true value; it is exactly the *true* value. > + <snipped> > +Memory profiler is expected to be thread safe, so it has a corresponding > +lock/unlock at internal mutex whenever you call corresponding memprof > +functions. If you want to build LuaJIT without thread safety use > +`-DLUAJIT_DISABLE_THREAD_SAFE`. This is not implemented in scope of the MVP, so drop this part. > + > +### Reading and displaying saved data > + > +Binary data can be read by `lj-parse-memprof` utility. It parses the binary Typo: s/lj-parse-memprof/luajit-parse-memprof/. > +format provided by memory profiler and render it on human-readable format. Typo: s/it on/it to/. > + <snipped> > +This table shows performance deviation in relation to REFerence value (before > +commit) with stopped and running profiler. The table shows the average value > +for 11 runs. The first field of the column indicates the change in the average > +time in seconds (less is better). The second field is the standard deviation > +for the found difference. > + > +``` > + Name | REF | AFTER, memprof off | AFTER, memprof on > +----------------+------+--------------------+------------------ > +array3d | 0.21 | +0.00 (0.01) | +0.00 (0.01) > +binary-trees | 3.25 | -0.01 (0.06) | +0.53 (0.10) > +chameneos | 2.97 | +0.14 (0.04) | +0.13 (0.06) > +coroutine-ring | 1.00 | +0.01 (0.04) | +0.01 (0.04) > +euler14-bit | 1.03 | +0.01 (0.02) | +0.00 (0.02) > +fannkuch | 6.81 | -0.21 (0.06) | -0.20 (0.06) > +fasta | 8.20 | -0.07 (0.05) | -0.08 (0.03) Side note: Still curious how this can happen. It looks OK when this is negative difference in within its deviation. But this is sorta magic. > +life | 0.46 | +0.00 (0.01) | +0.35 (0.01) > +mandelbrot | 2.65 | +0.00 (0.01) | +0.01 (0.01) > +mandelbrot-bit | 1.97 | +0.00 (0.01) | +0.01 (0.02) > +md5 | 1.58 | -0.01 (0.04) | -0.04 (0.04) > +nbody | 1.34 | +0.00 (0.01) | -0.02 (0.01) > +nsieve | 2.07 | -0.03 (0.03) | -0.01 (0.04) > +nsieve-bit | 1.50 | -0.02 (0.04) | +0.00 (0.04) > +nsieve-bit-fp | 4.44 | -0.03 (0.07) | -0.01 (0.07) > +partialsums | 0.54 | +0.00 (0.01) | +0.00 (0.01) > +pidigits-nogmp | 3.47 | -0.01 (0.02) | -0.10 (0.02) > +ray | 1.62 | -0.02 (0.03) | +0.00 (0.02) > +recursive-ack | 0.20 | +0.00 (0.01) | +0.00 (0.01) > +recursive-fib | 1.63 | +0.00 (0.01) | +0.01 (0.02) > +scimark-fft | 5.72 | +0.06 (0.09) | -0.01 (0.10) > +scimark-lu | 3.47 | +0.02 (0.27) | -0.03 (0.26) > +scimark-sor | 2.34 | +0.00 (0.01) | -0.01 (0.01) > +scimark-sparse | 4.95 | -0.02 (0.04) | -0.02 (0.04) > +series | 0.95 | +0.00 (0.02) | +0.00 (0.01) > +spectral-norm | 0.96 | +0.00 (0.02) | -0.01 (0.02) > +``` > -- > 2.28.0 > -- Best regards, IM
next prev parent reply other threads:[~2021-01-15 13:14 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-12-25 11:34 Sergey Kaplun 2021-01-15 13:14 ` Igor Munkin via Tarantool-discussions [this message] 2021-01-20 8:19 ` Sergey Kaplun via Tarantool-discussions 2021-01-20 14:26 ` Sergey Ostanevich via Tarantool-discussions 2021-01-20 14:57 ` Sergey Kaplun via Tarantool-discussions 2021-01-21 18:41 ` Igor Munkin via Tarantool-discussions 2021-01-21 18:42 ` Igor Munkin via Tarantool-discussions
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