5 ms·

Firefox has done this since forever. It's why official builds will generally be faster than compiling from scratch yourself. I'm surprised Chrome wasn't already

Firefox has done this since forever. It's why official builds will generally be faster than compiling from scratch yourself. I'm surprised Chrome wasn't already taking advantage of PGO.

3pt14159 6y ago
I'm surprised that there isn't a way to do PGO when compiling from scratch. A way of telling the compiler exactly what parts are, but build it into the codebase so that one could get the best of both worlds.
- mintplant 6y ago
  You can pass a PGO flag to the build system [0], but IIRC from when I was there last, Mozilla puts some serious machine hours into PGO cycles for each release and that isn't easy to replicate as an individual developer. The profiling captures things which are very specific to the actual build being optimized, so inlining that information into the codebase wouldn't be so helpful. Though there are already static optimization hints spread throughout the code (off the top of my head, MOZ_LIKELY/MOZ_UNLIKELY for marking conditionals). [0] https://firefox-source-docs.mozilla.org/build/buildsystem/pgo.html https://firefox-source-docs.mozilla.org/build/buildsystem/pg...
  - loeg 6y ago
    Mozilla could publish their profile data for a given release image.
    - glandium 6y ago
      They are public, but you have to know where to look. I do think they should be published alongside the builds on archive.mozilla.org. (disclaimer: I work for Mozilla)
  - CalChris 6y ago
    Given PGO and branch prediction, has anyone tested whether turning off MOZ_LIKELY/MOZ_UNLIKELY makes any difference?
- loeg 6y ago
  If someone can give you the PGO profile data from the exact same compiler and sources, you can do -fprofile-use (PGO) on subsequent builds.
  - rurban 6y ago
    Nowadays you are using perf profiles, and then use this with autofdo. The old -fprofile-use is not good enough and needs two steps.
- wyldfire 6y ago
  PGO guides inlining and branch prediction IIRC. You can give static hints about each of these. But the hints aren't on a continuum like they are with PGO. So finding an optimal balance for these will be harder. Also you have to maintain these hints. So if you were somehow giving hints with a hotness ratio in the source it would be impossible to maintain and keep it accurate.
  - brandmeyer 6y ago
    Also hot/cold partitioning. Keeping cold code code away from hot code can help L1I cache utilization, iTLB utilization, Operating system page-out, etc.
- 1f60c 6y ago
  This isn't the same, but some compilers have support for macros that tell it which branches are more likely to be taken than others, and in C++20, it's even a language feature.
- rurban 6y ago
  The G stands for guide. You need a testsuite to create a guided profile to optimize the branch hints. Normally there's a simple make target, like chrome.pgo to create the initial binary chrome, run the testsuite with pgo or better autofdo via perf and from this create the optimized chrome.pgo. using Facebook's bolt is even better. I have no idea about Google's byzantinian bazel tool. With make it's a simple target which automates these steps.
Klathmon 6y ago
>It's why official builds will generally be faster than compiling from scratch yourself. Would it be possible for Google to publish the profile data along with the source code to enable those who compile from scratch to have these same optimizations? >I'm surprised Chrome wasn't already taking advantage of PGO. They have been on windows since M53 (released in 2016), but this seems to be a better implementation and it's now for MacOS as well now.
- loeg 6y ago
  Is M85 the first Chrome Windows release done with Clang, as opposed to MSVC? I haven't been following the Windows side of it.
  - Ziggy_Zaggy 6y ago
    Great question! Anyone have this answer?
    - zmodem 6y ago
      Chrome M64 was the first shipping version built with Clang on Windows: http://web.archive.org/web/20200125010517/http://blog.llvm.org/2018/03/clang-is-now-used-to-build-chrome-for.html http://web.archive.org/web/20200125010517/http://blog.llvm.o...
      - loeg 6y ago
        Thanks. So Chrome on Windows had MSVC PGO from 53-63, but lost PGO from 64-84.
- CalChris 6y ago
  Can you explain this because the article says: It is rolling out with Chrome M85 on Mac and Windows. Never mind. This [1] says: Starting in Chrome 53, Chrome has started using Microsoft’s Profile Guided Optimization (PGO) technology to make Chrome up to 15% faster on Windows. This strongly implies Google was using MSVC for the M53 build. [1] https://blog.chromium.org/2016/10/making-chrome-on-windows-faster-with-pgo.html https://blog.chromium.org/2016/10/making-chrome-on-windows-f...
Scarbutt 6y ago
And yet, Chrome has always feeled snappier and faster.
- michaelmrose 6y ago
  Chrome adopted multi core far sooner. A great if lengthy treatment here https://yoric.github.io/post/why-did-mozilla-remove-xul-addons/ https://yoric.github.io/post/why-did-mozilla-remove-xul-addo...
deleted 6y ago
[deleted]
Lammy 6y ago
I do PROFILE=on for my own www/firefox FreeBSD package builds too, but it does make it take twice as long. https://www.freshports.org/www/firefox https://www.freshports.org/www/firefox
crawsome 6y ago
It's going to take a LOT of convincing to get me to use Chrome. I don't trust an ad company as my internet browser or phone OS anymore.
cpeterso 6y ago
Firefox started using PGO on Windows in Firefox in 2008 [1], Android last year [2], and macOS earlier this year [3]. Firefox uses PGO on Linux, but I don't remember when it was enabled. [1] https://bugzilla.mozilla.org/show_bug.cgi?id=418865 https://bugzilla.mozilla.org/show_bug.cgi?id=418865 [2] https://bugzilla.mozilla.org/show_bug.cgi?id=632954 https://bugzilla.mozilla.org/show_bug.cgi?id=632954 [3] https://bugzilla.mozilla.org/show_bug.cgi?id=1604578 https://bugzilla.mozilla.org/show_bug.cgi?id=1604578
- ignoramous 6y ago
  /offtopic The all-new Firefox for Android (codename Daylight) is lightening fast, and perceptibly seems on-par with the Chrome for Android in terms of responsiveness. What stumps me is Chrome for Android is 3.8MB whereas Firefox Daylight is upwards of 40MB.
  - outworlder 6y ago
    Not sure if they will keep this edge given all the loss of talent.
  - elisaado 6y ago
    Chrome's engine is built into Android, whereas the engine Firefox uses is not and thus has to be shipped with it.
  - agi0 6y ago
    I haven't looked at what Google does recently but you're likely getting most of Chrome in a separate package (e.g. the system WebView). Chrome and Firefox are of compareble size IIRC (56MB vs 65MB)
  - avasthe 6y ago
    What's sad is they only support very few selected Add Ons.
vffhfhf 6y ago
Not a glowing review of firefox lol.
cromwellian 6y ago
Chrome's been doing it for a long time too, since version 53.

Firefox has done this since forever. It's why official builds will generally be faster than compiling from scratch yourself. I'm surprised Chrome wasn't already taking advantage of PGO.

3pt14159 6y ago

I'm surprised that there isn't a way to do PGO when compiling from scratch. A way of telling the compiler exactly what parts are, but build it into the codebase so that one could get the best of both worlds.

mintplant 6y ago
You can pass a PGO flag to the build system [0], but IIRC from when I was there last, Mozilla puts some serious machine hours into PGO cycles for each release and that isn't easy to replicate as an individual developer. The profiling captures things which are very specific to the actual build being optimized, so inlining that information into the codebase wouldn't be so helpful. Though there are already static optimization hints spread throughout the code (off the top of my head, MOZ_LIKELY/MOZ_UNLIKELY for marking conditionals). [0] https://firefox-source-docs.mozilla.org/build/buildsystem/pgo.html https://firefox-source-docs.mozilla.org/build/buildsystem/pg...
- loeg 6y ago
  Mozilla could publish their profile data for a given release image.
  - glandium 6y ago
    They are public, but you have to know where to look. I do think they should be published alongside the builds on archive.mozilla.org. (disclaimer: I work for Mozilla)
- CalChris 6y ago
  Given PGO and branch prediction, has anyone tested whether turning off MOZ_LIKELY/MOZ_UNLIKELY makes any difference?
loeg 6y ago
If someone can give you the PGO profile data from the exact same compiler and sources, you can do -fprofile-use (PGO) on subsequent builds.
- rurban 6y ago
  Nowadays you are using perf profiles, and then use this with autofdo. The old -fprofile-use is not good enough and needs two steps.
wyldfire 6y ago
PGO guides inlining and branch prediction IIRC. You can give static hints about each of these. But the hints aren't on a continuum like they are with PGO. So finding an optimal balance for these will be harder. Also you have to maintain these hints. So if you were somehow giving hints with a hotness ratio in the source it would be impossible to maintain and keep it accurate.
- brandmeyer 6y ago
  Also hot/cold partitioning. Keeping cold code code away from hot code can help L1I cache utilization, iTLB utilization, Operating system page-out, etc.
1f60c 6y ago
This isn't the same, but some compilers have support for macros that tell it which branches are more likely to be taken than others, and in C++20, it's even a language feature.
rurban 6y ago
The G stands for guide. You need a testsuite to create a guided profile to optimize the branch hints. Normally there's a simple make target, like chrome.pgo to create the initial binary chrome, run the testsuite with pgo or better autofdo via perf and from this create the optimized chrome.pgo. using Facebook's bolt is even better. I have no idea about Google's byzantinian bazel tool. With make it's a simple target which automates these steps.

Klathmon 6y ago

>It's why official builds will generally be faster than compiling from scratch yourself. Would it be possible for Google to publish the profile data along with the source code to enable those who compile from scratch to have these same optimizations? >I'm surprised Chrome wasn't already taking advantage of PGO. They have been on windows since M53 (released in 2016), but this seems to be a better implementation and it's now for MacOS as well now.

loeg 6y ago
Is M85 the first Chrome Windows release done with Clang, as opposed to MSVC? I haven't been following the Windows side of it.
- Ziggy_Zaggy 6y ago
  Great question! Anyone have this answer?
  - zmodem 6y ago
    Chrome M64 was the first shipping version built with Clang on Windows: http://web.archive.org/web/20200125010517/http://blog.llvm.org/2018/03/clang-is-now-used-to-build-chrome-for.html http://web.archive.org/web/20200125010517/http://blog.llvm.o...
    - loeg 6y ago
      Thanks. So Chrome on Windows had MSVC PGO from 53-63, but lost PGO from 64-84.
CalChris 6y ago
Can you explain this because the article says: It is rolling out with Chrome M85 on Mac and Windows. Never mind. This [1] says: Starting in Chrome 53, Chrome has started using Microsoft’s Profile Guided Optimization (PGO) technology to make Chrome up to 15% faster on Windows. This strongly implies Google was using MSVC for the M53 build. [1] https://blog.chromium.org/2016/10/making-chrome-on-windows-faster-with-pgo.html https://blog.chromium.org/2016/10/making-chrome-on-windows-f...

Scarbutt 6y ago

And yet, Chrome has always feeled snappier and faster.

michaelmrose 6y ago
Chrome adopted multi core far sooner. A great if lengthy treatment here https://yoric.github.io/post/why-did-mozilla-remove-xul-addons/ https://yoric.github.io/post/why-did-mozilla-remove-xul-addo...

deleted 6y ago

[deleted]

Lammy 6y ago

I do PROFILE=on for my own www/firefox FreeBSD package builds too, but it does make it take twice as long. https://www.freshports.org/www/firefox https://www.freshports.org/www/firefox

crawsome 6y ago

It's going to take a LOT of convincing to get me to use Chrome. I don't trust an ad company as my internet browser or phone OS anymore.

cpeterso 6y ago

Firefox started using PGO on Windows in Firefox in 2008 [1], Android last year [2], and macOS earlier this year [3]. Firefox uses PGO on Linux, but I don't remember when it was enabled. [1] https://bugzilla.mozilla.org/show_bug.cgi?id=418865 https://bugzilla.mozilla.org/show_bug.cgi?id=418865 [2] https://bugzilla.mozilla.org/show_bug.cgi?id=632954 https://bugzilla.mozilla.org/show_bug.cgi?id=632954 [3] https://bugzilla.mozilla.org/show_bug.cgi?id=1604578 https://bugzilla.mozilla.org/show_bug.cgi?id=1604578

ignoramous 6y ago
/offtopic The all-new Firefox for Android (codename Daylight) is lightening fast, and perceptibly seems on-par with the Chrome for Android in terms of responsiveness. What stumps me is Chrome for Android is 3.8MB whereas Firefox Daylight is upwards of 40MB.
- outworlder 6y ago
  Not sure if they will keep this edge given all the loss of talent.
- elisaado 6y ago
  Chrome's engine is built into Android, whereas the engine Firefox uses is not and thus has to be shipped with it.
- agi0 6y ago
  I haven't looked at what Google does recently but you're likely getting most of Chrome in a separate package (e.g. the system WebView). Chrome and Firefox are of compareble size IIRC (56MB vs 65MB)
- avasthe 6y ago
  What's sad is they only support very few selected Add Ons.

vffhfhf 6y ago

Not a glowing review of firefox lol.

cromwellian 6y ago

Chrome's been doing it for a long time too, since version 53.