Re: [MirageOS-devel] Tracing and profiling blog post

[Thomas Leonard <talex5@xxxxxxxxx>]

On 27 October 2014 11:22, Anil Madhavapeddy <anil@xxxxxxxxxx> wrote:
> On 27 Oct 2014, at 11:17, Thomas Leonard <talex5@xxxxxxxxx> wrote:
>>
>> Note that everything should (in future) compile with an unmodified
>> Lwt. Pinning the tracing version of Lwt is what will trigger
>> everything to recompile with profiling support. So, getting this
>> upstream shouldn't block anything (and might indeed be difficult),
>> although if upstream wants to add a flag for it that would be great
>> too.
>>
>> This is a change to my previous plan of having Lwt depend on
>> mirage-profiling. Now, mirage-profiling depends on Lwt. If you want to
>> use any extended feature of Lwt you should go via profiling. e.g. in
>> mirage-platform we have:
>>
>> let ports = Array.init nr_events (fun port -> {
>>  counter = program_start;
>>  c = Profile.named_condition ("after-chn-" ^ string_of_int port)
>> })
>>
>> If Lwt.tracing is installed then Profile.named_condition is:
>>
>> let named_condition label =
>>  Lwt_condition.create ~label ()
>>
>> Without, it will be:
>>
>> let named_condition _label = Lwt_condition.create ()
>
> This also sounds like the right order, and permits other tracing
> strategies in the future for Lwt.  Are you doing the mirage-platform
> conditional compilation via optcomp?

My plan is that only mirage-profile will use conditional compilation
and everything else will always depend on mirage-profile, but get the
calls optimised out by the compiler when tracing isn't being used.

Currently though I haven't implemented anything. I was thinking of
having two versions of profile.ml and only compiling the appropriate
one.

mirage-profile is currently using assemblage, so any suggestions on
the best way to do that are welcome. My current thought is to have a
flag saying whether you want profiling, and have OPAM set the flag
depending on the availablilty of the lwt.tracing ocamlfind package
(which the modified Lwt installs). Or should the build detect this
somehow?

If assemblage is too experimental for mirage-dev, I could also convert to oasis.


-- 
Dr Thomas Leonard        http://0install.net/
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