- From: Chris Rogers <crogers@google.com>
- Date: Wed, 17 Jul 2013 11:41:50 -0700
- To: Srikumar Karaikudi Subramanian <srikumarks@gmail.com>
- Cc: "K. Gadd" <kg@luminance.org>, Jer Noble <jer.noble@apple.com>, Olivier Thereaux <Olivier.Thereaux@bbc.co.uk>, WG <public-audio@w3.org>
- Message-ID: <CA+EzO0==-rZYAUL5mHHS+22zQ75GM8+9qPH-ahqexu=DTacLVQ@mail.gmail.com>
On Tue, Jul 16, 2013 at 7:24 PM, Srikumar Karaikudi Subramanian < srikumarks@gmail.com> wrote: > Your hypothetical test case merely demonstrates the difference; my point > is that it is silly to optimize for imaginary edge cases at the cost of > real-world use cases where developers will get unexpected results due to > leaving race conditions in this API. I should also note that it has come up > in past discussions that we could always introduce new no-copy APIs that > don't contain races, if the cost of memcpy is so severe. > > > It is not inconceivable to make an audio editor which plays an audio file > from a specific sample onwards by assigning the buffer to an > AudioBufferSourceNode and using start(t,offset,duration) ... possibly > followed by effects. Large files (even 5mins?) would be unusable with such > an editor if a copy were involved and clients/devs will be forced to do > crazy optimizations just to get it to work. Now shift that situation to an > iPad with limited memory and it can get worse. DAWs are a use case for the > API. > > With Jer's example code, it would be possible to simulate such a > (reasonable) case. > > What might, I think, be acceptable is a one-time copy provided the copy > can be reused without additional cost. As far as I can see, immutable data > structures are the best candidates to solve the race conditions. > > That said, I do find the argument (I think Rogers') that the worst thing > that can happen with these race conditions is unexpected audio output and > hence they are not very important an interesting stand. > You're simplifying my position a bit. What I'm saying is there are no sensible or normal calling patterns where this type of race conditions is even a possibility. As the API is designed and has been used for over 2 years, these calling patterns are not used and so simply are not an issue. We do have substantial developer experience to support this view, and these developers come from a wide range of backgrounds and experience levels from complete novices playing with audio for the first time, all the way to seasoned professional audio developers. Chris > > -Kumar > > On 17 Jul, 2013, at 7:13 AM, "K. Gadd" <kg@luminance.org> wrote: > > Of course you can claim hypothetical performance benefits from any > particular optimization, my point is that in this case we're considering > whether or not to leave *race conditions* in a new Web API because we think > it might make it faster. We *think* it *might*. Making that sort of > sacrifice in favor of 'performance' without doing any reproducible, > remotely scientific testing to see whether it's actually faster, let alone > fast enough to justify the consequences, seems rash to me. > > It should be quite easy to test the performance benefits of the racy > version of the API, as based on my understanding the Firefox implementation > currently makes copies. You need only run your test cases in Firefox with > SPS and see how much time is spent making calls to memcpy to get a rough > picture of the actual overhead. And once you know that, you can look at how > your test cases actually perform and see if the cost of that memcpy makes > it impossible to ship an implementation that makes those copies. > > I am literally unable to imagine a use case where the cost of the copies > would add up to the point where it would remotely be considered a > bottleneck. It is the case that the copies probably have to be synchronous, > so I could see this hurting the ability to trigger tons and tons of sounds > in a single 'frame' from JS, or set tons and tons of curves, etc. But > still, memcpy isn't that slow, especially for small numbers of bytes. > > Your hypothetical test case merely demonstrates the difference; my point > is that it is silly to optimize for imaginary edge cases at the cost of > real-world use cases where developers will get unexpected results due to > leaving race conditions in this API. I should also note that it has come up > in past discussions that we could always introduce new no-copy APIs that > don't contain races, if the cost of memcpy is so severe. > > > On Tue, Jul 16, 2013 at 6:27 PM, Jer Noble <jer.noble@apple.com> wrote: > >> >> On Jul 16, 2013, at 1:18 PM, K. Gadd <kg@luminance.org> wrote: >> >> This claim has been made dozens of times now on the list and I've seen >> multiple requests for even a single test case that demonstrates the >> performance impact. Is there one? I haven't seen one, nor a comment to the >> effect that one exists, or an explanation of why there isn't one. >> >> >> Isn't this self-evident? Any solution which involves additional memcopy >> calls during the normal use of the API will have an inherant and known >> performance cost at the point of the memcopy. Additionally, there is the >> ongoing performance cost of having duplicate, in-memory copies of audio >> data, as well as the additional GC cost of those extra copies. >> >> That said, it would be very easy to demonstrate: in the hypothetical test >> case, create a new ArrayBuffer from source data before passing it into the >> API. I.e., >> >> sourceNode.buffer = buffer >> >> >> becomes: >> >> sourceNode.buffer = buffer.slice(0) >> >> >> -Jer >> > > >
Received on Wednesday, 17 July 2013 18:42:18 UTC