On Tue, Sep 11, 2018 at 04:42:09PM +0300, Alexey Budankov wrote: > Hi, > > On 11.09.2018 11:34, Jiri Olsa wrote: > > On Tue, Sep 11, 2018 at 11:16:45AM +0300, Alexey Budankov wrote: > >> > >> Hi Ingo, > >> > >> On 11.09.2018 9:35, Ingo Molnar wrote: > >>> > >>> * Alexey Budankov <[email protected]> wrote: > >>> > >>>> It may sound too optimistic but glibc API is expected to be backward > >>>> compatible > >>>> and for POSIX AIO API part too. Internal implementation also tends to > >>>> evolve to > >>>> better option overtime, more probably basing on modern kernel > >>>> capabilities > >>>> mentioned here: http://man7.org/linux/man-pages/man2/io_submit.2.html > >>> > >>> I'm not talking about compatibility, and I'm not just talking about > >>> glibc, perf works under > >>> other libcs as well - and let me phrase it in another way: basic event > >>> handling, threading, > >>> scheduling internals should be a *core competency* of a tracing/profiling > >>> tool. > >> > >> Well, the requirement of independence from some specific libc > >> implementation > >> as well as *core competency* design approach clarify a lot. Thanks! > >> > >>> > >>> I.e. we might end up using the exact same per event fd thread pool design > >>> that glibc uses > >>> currently. Or not. Having that internal and open coded to perf, like Jiri > >>> has started > >>> implementing it, allows people to experiment with it. > >> > >> My point here is that following some standardized programming models and > >> APIs > >> (like POSIX) in the tool code, even if the tool itself provides internal > >> open > >> coded implementation for the APIs, would simplify experimenting with the > >> tool > >> as well as lower barriers for new comers. Perf project could benefit from > >> that. > >> > >>> > >>> This isn't some GUI toolkit, this is at the essence of perf, and we are > >>> not very good on large > >>> systems right now, and I think the design should be open-coded threading, > >>> not relying on an > >>> (perf-)external AIO library to get it right. > >>> > >>> The glibc thread pool implementation of POSIX AIO is basically a > >>> fall-back > >>> implementation, for the case where there's no native KAIO interface to > >>> rely on. > >>> > >>>> Well, explicit threading in the tool for AIO, in the simplest case, > >>>> means > >>>> incorporating some POSIX API implementation into the tool, avoiding > >>>> code reuse in the first place. That tends to be error prone and costly. > >>> > >>> It's a core competency, we better do it right and not outsource it. > >> > >> Yep, makes sense. > > > > on the other hand, we are already trying to tie this up under perf_mmap > > object, which is what the threaded patchset operates on.. so I'm quite > > confident that with little effort we could make those 2 things live next > > to each other and let the user to decide which one to take and compare > > > > possibilities would be like: (not sure yet the last one makes sense, but > > still..) > > > > # perf record --threads=... ... > > # perf record --aio ... > > # perf record --threads=... --aio ... > > > > how about that? > > That might be an option. What is the semantics of --threads?
that's my latest post on this: https://marc.info/?l=linux-kernel&m=151551213322861&w=2 working on repost ;-) jirka > > Be aware that when experimenting with serial trace writing on an 8-core > client machines running an HPC benchmark heavily utilizing all 8 cores > we noticed that single Perf tool thread contended with the benchmark > threads. > > That manifested like libiomp.so (Intel OpenMP implementation) functions > appearing among the top hotspots functions and this was indication of > imbalance induced by the tool during profiling. > > That's why we decided to first go with AIO approach, as it is posted, > and benefit from it the most thru multi AIO, prior turning to more > resource consuming multi-threading alternative. > > > > > I just rebased the thread patchset, will make some tests (it's been few > > months, > > so it needs some kicking/checking) and post it out hopefuly this week> > > jirka > >
