# Will Robert Love's new HZ patch make it into 1.4?

## Freek

Hi,

First, i'm new to the forums so please bare with me if i'm posting wrong somehow.

Robert Love has backported his HZ patch to the 2.4 kernel. As this is a performance patch _and_ Gentoo has a performance reputation to keep up, I wondered if this patch wil make it in Gentoo 1.4 or maybe it's allready in! I searched everywhere but I didn't find any references to it.

Cheers,

Fred van Zwieten (Freek)

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## rac

Is this patch substantially different from 

```
XX_jiffies-for-i386-2*

From the Linux-Kernel Mailing List

This patch allows the user to configure the

jiffies value for the linux kernel.

Jiffies is how many times per second the kernel

listens to the clock interrupt to check for

things like preemption, completion of dma

transfers, and the need to reschedule.  By

allowing the user to confgure this, we can let

the user optimize their timing for either a

realtime environment or a higher throughput

environment.
```

 :Question: 

This one has been in gentoo-sources for some time now.

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## Freek

We'll, it sure looks like it's the same. The article on kerneltrap suggested it was a recent backport and I could not find any reference, so I thought i'd ask.

Well, if it's in, it's in, and that's good i guess   :Smile: 

Cheers,

Fred van Zwieten (Freek)

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## Lovechild

what rml backported, wasn't really a timer fix for jiffies?

Because changing jiffy setting could, and would screw up the clock?

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## arkane

The thing that bothers me the most about this patch is the limitation of ~49 days uptime.

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## Freek

We'll, as I read it, the uptime reporting cycles every ~49 days, so if you don't bother about that, there's no problem.

I am confused however, according to rac the patch seemed to be allready included in gentoo-sources "for some time now". Doesn't that mean we should also have the ~49 days uptime issue?

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## arkane

 *Freek wrote:*   

> We'll, as I read it, the uptime reporting cycles every ~49 days, so if you don't bother about that, there's no problem.
> 
> I am confused however, according to rac the patch seemed to be allready included in gentoo-sources "for some time now". Doesn't that mean we should also have the ~49 days uptime issue?

 

The way I was reading it, it effected both the reporting and the system... with one user actually reaching the ~479 day mark of the current 100 jiffy and having the registers dumped.

(this was on kerneltrap)

But yeah, if the patch is in the gentoo-sources, it would be effected by the 49 day limitation.  I haven't used gentoo for a server (debian on my server, Gentoo for the desktop) so I haven't had my system up long enough to test the problem.

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## rac

 *Freek wrote:*   

> I am confused however, according to rac the patch seemed to be allready included in gentoo-sources "for some time now". Doesn't that mean we should also have the ~49 days uptime issue?

 

I was too lazy to track it down, and I didn't use gentoo-sources until 2.4.19-r10, but I remember reading people posting about jiffies settings in older versions ... [search search] ... yes, searching for "jiffies" brings up several threads, with people posting about 2.4.19-r7, so the option has been in there since at least early June.  I would assume that anybody using it would be susceptible to the uptime overflow condition.

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## Freek

Well, maybe the 64bit-jiffies backport is also in. The discussion on the kerneltrap article is not clear on this being a actual problem. There are reports on succesfull and unsuccesfull jiffies wraparounds

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## Mnemia

Well, I've got a server running gentoo-sources that will reach that limit in about a week and a half...if no one has figured this out by then I'll post back.

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## arkane

 *Mnemia wrote:*   

> Well, I've got a server running gentoo-sources that will reach that limit in about a week and a half...if no one has figured this out by then I'll post back.

 

That would be very cool.  Then, at least we'll know for sure:)

I use vanilla sources, so unfortunately (fortunately?) I don't have the ability to recreate this.

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## Pigeon

Seems some gentoo users have encountered this in this thread.  System didn't crash but it was fairly confusing.  :Laughing: 

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## Freek

Okay, that sure seemes to confirm the jiffies patch is in. Anyone knows wether the 64bit jiffies will be in anytime soon, because that wil solve it kind of permanently.

From the other thread it looks like the box will survive a wraparound, but it's just, well, ugly. I can image some drivers will go crazy on it.

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## Mnemia

Yes, I can confirm that it does roll over at 49 days. I concur with the other posters.

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## faz

Okay, perhaps there is a possibility to include the 64 bit jiffies backport in 1.4 so this confusion end's. It seems that not _all_ drivers are okay with a rollover, so it depend's on you're config whether this is a problem or not.

Any idea how to request the gentoo developers for inclusion?

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## Mnemia

File a bug in bugzilla and ask on the mailing lists; they're much more likely to read about it there than here in the forums. 

When my server rolled over at 49 days, I didn't notice anything "not working", but then there could have been something subtle I didn't find in my cursory inspection (I've since rebooted it). As you've said, it's likely dependent on configuration. It should be fixed, though it's not a huge problem as long as people who are running servers that don't get rebooted often are aware of this limitation of those kernels. Perhaps a prominent mention in the install docs would be in order if a backport is not immediately feasible.

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## faz

Oke, i'll file a bug as soon as I can find the time. Thanx for the efforts

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## meekjt

Hello. What happens when the uptime rolls over? I'm using gentoo-sources 2.4.19-r9 with an uptime of  50 days, 11:16.

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## masseya

According to the thread that was linked to above, it seems as though it just resets your uptime.

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## faz

There are also some reports about instabilities occuring and that's a Bad Thing. btw, i've requested inclusion of the 64bit jiffies in bugzilla.

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