High CPU usage of WebKit... process

[iirekm]

Version

latest

Operating System

macOS

Distribution Method

dmg (Mac OS - Apple Silicon)

Describe the issue

Workaround: WEBKIT_DISABLE_COMPOSITING_MODE=1
OS: Kubuntu 24

However it's a shame it exists, most users won't be able to figure that out

How to reproduce (Optional)

No response

Expected behavior (Optional)

No response

Relevant log output (Optional)

[slarse]

Hello!

This is a good find, thanks for reporting!

I've been working with improving things with the Linux distributions. You've reported macOS and dmg as your OS and distribution method, but then the description says Kubuntu 24, so I'm guessing you're on the latter? Which package format are you using, and what do you mean by "latest" version? Are you building from master? Using nightly 0.5.1760? An exact version is helpful :)

I've been toying around on a few different machines, and at first glance it does appear as if disabling hardware acceleration (WEBKIT_DISABLE_COMPOSITING_MODE=1) decreases baseline CPU usage. However, this is a small sample size and different versions of WebkitGTK and different hardware and operating systems might have wildly different reactions to it. Disabling hardware acceleration should in general make performance worse.

On my machines, I've narrowed down the issue to the new-ish DMA-Buf renderer which seems to not be performing well. Would you mind trying to disable that and see if that has a similar effect on performance for you?

Simply set this environment variable when running the app:

WEBKIT_DISABLE_DMABUF_RENDERER=1

Setting any of these variables in the app itself is a bit of a scary proposition without testing on a whole bunch of machines (I only have 3 at hand). But we could absolutely add these environment variables as suggestions in LINUX.md.

[slarse]

Actually, looking into the source code of WebkitGTK, it appears as if WEBKIT_DISABLE_DMABUF_RENDERER=1 also completely disables hardware acceleration.

WEBKIT_DISABLE_COMPOSITING_MODE is evaluated here.

    const char* disableCompositing = getenv("WEBKIT_DISABLE_COMPOSITING_MODE");
    if ((disableCompositing && strcmp(disableCompositing, "0")) || !AcceleratedBackingStore::checkRequirements())
        m_canUseHardwareAcceleration = false;

Note the || !AcceleratedBackingStore::checkRequirements(). checkRequirements() returns false if, among other things, we can't find renderer mode.

bool AcceleratedBackingStore::checkRequirements()
{
    if (!rendererBufferTransportMode().isEmpty())
        return gtkCanUseHardwareAcceleration();
    return false;
}

And the first thing that causes us to not find a renderer mode is apparently if WEBKIT_DISABLE_DMABUF_RENDERER is set.

        const char* disableDMABuf = getenv("WEBKIT_DISABLE_DMABUF_RENDERER");
        if (disableDMABuf && g_strcmp0(disableDMABuf, "0"))
            return;

So, unless I'm completely missing something, there's currently no difference between disabling the DMA-Buf renderer or explicitly disabling hardware acceleration, they have the same effect. Perhaps they differed in the past, the blog post I linked above suggest they did.

I will try this out for a while on a few different machines and report back with what I find. Thanks again for the pointer @iirekm!