An MGLRU Performance Regression Fix Is On The Way Plus Another Optimization

[phoronix]

Phoronix: An MGLRU Performance Regression Fix Is On The Way Plus Another Optimization

While MGLRU is a nice performance win for the Linux kernel now available when enabling it for v6.1+ kernel builds, during my testing I did encounter a regression around the SVT-AV1 video encode performance at least and a fix is working its way toward mainline...

https://www.phoronix.com/news/MGLRU-SVT-Performance-Fix

[Danny3]

Great, but I hope it didn't made other tests to regress as I could've lived just fine with only this test regressing.
I wonder when will they enable MGLRU by default or at least provide a way to enable it through kernel boot parameters.

[coder]

Good job, Michael and [email protected] !

[[email protected]]

Good job, Michael and [email protected] !

Thank you. And happy new year!

[FPScholten]

Great, but I hope it didn't made other tests to regress as I could've lived just fine with only this test regressing.
I wonder when will they enable MGLRU by default or at least provide a way to enable it through kernel boot parameters.

To see if it is enabled use the following:

cat /sys/kernel/mm/lru_gen/enabled

if this is 0 mglru is disabled 1 up to 7 means it is enabled, 7 is with all features on, for exact specifications, read the documentation. Most users should enable all functions.
To enable mglru with all functions on use the following as root:

echo y >/sys/kernel/mm/lru_gen/enabled

To disable substitute y with 0, to limit functionality substitute y with a number between 1 and 7

[Linuxxx]

To see if it is enabled use the following:

cat /sys/kernel/mm/lru_gen/enabled

if this is 0 mglru is disabled 1 up to 7 means it is enabled, 7 is with all features on, for exact specifications, read the documentation. Most users should enable all functions.
To enable mglru with all functions on use the following as root:

echo y >/sys/kernel/mm/lru_gen/enabled

To disable substitute y with 0, to limit functionality substitute y with a number between 1 and 7

I really hope for your own sanity that you aren't running that command manually upon every (re)boot yourself...

Just in case, here's how it will automagically run on every start-up, guaranteed:

cat << EOF | sudo tee /etc/udev/rules.d/99-mglru.rules
RUN+="/bin/bash -c '/bin/echo 7 > /sys/kernel/mm/lru_gen/enabled'"
EOF

You're welcome!

And for those who believe that a systemd service file would be more adequate:

No, because it is unable to reliably set the desired values under /sys/, meaning that on some boot-ups it will be set correctly, while other times it won't (already tried myself).

[coder]

And for those who believe that a systemd service file would be more adequate:

No, because it is unable to reliably set the desired values under /sys/, meaning that on some boot-ups it will be set correctly, while other times it won't (already tried myself).

Why is this? Is there a race condition vs. another service which also sets it? If so, a dependency would fix that, but it suggests there might actually be another, better way to set it.

[intelfx]

And for those who believe that a systemd service file would be more adequate:

No, because it is unable to reliably set the desired values under /sys/, meaning that on some boot-ups it will be set correctly, while other times it won't (already tried myself).

This sounds bogus. There is no reason why systemd (or, more precisely, systemd-launched processes) should be unable to reliably set values in sysfs.

That said, using tmpfiles is preferable to both custom udev rules and custom systemd services.

[FPScholten]

I really hope for your own sanity that you aren't running that command manually upon every (re)boot yourself...

Just in case, here's how it will automagically run on every start-up, guaranteed:


You're welcome!

And for those who believe that a systemd service file would be more adequate:

No, because it is unable to reliably set the desired values under /sys/, meaning that on some boot-ups it will be set correctly, while other times it won't (already tried myself).

No much simpler, I have it enabled by default in my kernel parameters

CONFIG_LRU_GEN_ENABLED=y

If for some reason I want to temporarily disable it, or reduce the features, my commands are useful for that.

[Danny3]

To see if it is enabled use the following:

cat /sys/kernel/mm/lru_gen/enabled

if this is 0 mglru is disabled 1 up to 7 means it is enabled, 7 is with all features on, for exact specifications, read the documentation. Most users should enable all functions.
To enable mglru with all functions on use the following as root:

echo y >/sys/kernel/mm/lru_gen/enabled

To disable substitute y with 0, to limit functionality substitute y with a number between 1 and 7

Wonderful, thank you very much for such a detailed and well explained answer!

I really hope for your own sanity that you aren't running that command manually upon every (re)boot yourself...

Just in case, here's how it will automagically run on every start-up, guaranteed:


You're welcome!

And for those who believe that a systemd service file would be more adequate:

No, because it is unable to reliably set the desired values under /sys/, meaning that on some boot-ups it will be set correctly, while other times it won't (already tried myself).

Thank you very much!