<div dir="ltr"><div>On Wed, May 7, 2014 at 4:37 PM, Ryosuke Niwa <span dir="ltr"><<a href="mailto:rniwa@webkit.org" target="_blank">rniwa@webkit.org</a>></span> wrote:<br></div><div class="gmail_extra"><div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div class="h5">On Wed, May 7, 2014 at 4:36 PM, Ryosuke Niwa <span dir="ltr"><<a href="mailto:rniwa@webkit.org" target="_blank">rniwa@webkit.org</a>></span> wrote:<br>
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<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>On Mon, May 5, 2014 at 8:02 PM, Rik Cabanier <span dir="ltr"><<a href="mailto:cabanier@gmail.com" target="_blank">cabanier@gmail.com</a>></span> wrote:<br>
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<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">On Mon, May 5, 2014 at 6:23 PM, Oliver Hunt <span dir="ltr"><<a href="mailto:oliver@apple.com" target="_blank">oliver@apple.com</a>></span> wrote:<br>
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<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div style="word-wrap:break-word">On May 5, 2014, at 6:13 PM, Rik Cabanier <<a href="mailto:cabanier@gmail.com" target="_blank">cabanier@gmail.com</a>> wrote:<div>
<div><blockquote type="cite"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div style="word-wrap:break-word"><div>Do you really want a page to know that you have a fancy-pants 24-core Mac Pro rather than a little Mac mini?</div>
</div></blockquote><div><br></div><div>Yes!</div><div>If I have 24 cores ready to do work and the page can put them to use, I would like it to do so.</div><div>At the same time, if I just have a old mac mini, I don't want the page to launch 24 workers as that will exhaust my memory and cause contention. </div>
</div></div></div></blockquote><div><br></div></div><div>But I don't have 24 cores available, i have 24 cores installed. You have no idea what the actual workload of the system is, you don't know whether any other tabs are also using workers, you only have one piece of information, and that is nowhere near sufficient to make a reasonable choice.</div>
</div></div></blockquote><div><br></div></div><div>Sure, if I have 2 tabs and each one consumes all my CPU resources, things will run at half the speed and maybe even worse because of we would use more memory.</div></div>
</div></div></blockquote><div><br></div></div><div>At most at half the speed; it could be significantly worse if each worker ended up accessing completely different parts of RAM, etc...</div><div><br></div><div>Furthermore, the performance characteristics of 4 physical cores with SMT enabled for the total of 8 logical cores is substantially different from that of a system with 4 physical cores without SMT (4 logical) or 8 physical cores without SMT (8 logical). In some cases, distributing work among 8 threads concurrently in such a system (4 physical cores with SMT) results in a much worse performance than doing so among 4 threads.</div>
<div></div></div><br></div><div class="gmail_extra">So while I agree that providing some API to let developers know of the number of threads that could be ran concurrently</div></div></blockquote><div><br></div></div></div>
<div>is useful</div><div class="">
<div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra">, I'm not certain the number of installed cores is a good metrics for that.</div>
</div></blockquote></div></div></div></div></blockquote><div><br></div><div>I'll throw in another point that waking up all physical cores may result in a higher power usage compared to running the exact same task in a single core for a longer period of time. So we may need to take that into account as well.</div>
<div><br></div><div>How about exposing something like the number of preferred concurrent threads, which UA can adjust dynamically and maybe have an event that notifies that the value has changed.</div><div><br></div><div>
- R. Niwa</div><div><br></div></div></div></div>