Kernel 2.4.x and 2.4.1-preX - Higher latency then 2.2.x kernels?

Kernel 2.4.x and 2.4.1-preX - Higher latency then 2.2.x kernels?

[Shawn Starr]

It it just me or does it seem that 2.4.x has some latency problems?

It just seems that since using 2.4 ive noticed my poor Pentium 200Mhz
slow down whether being in X or otherwise. It just seems that the system
is sluggish.

I am using the new ReiserFS filesystem and I do know its still in heavy
development perhaps my latency is due to this (?)

Any suggestions?

Shawn.


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Re: Kernel 2.4.x and 2.4.1-preX - Higher latency then 2.2.x kernels?

[Gregory Maxwell]

On Sat, Jan 20, 2001 at 02:50:16PM -0500, Shawn Starr wrote: 
> It just seems that since using 2.4 ive noticed my poor Pentium 200Mhz
> slow down whether being in X or otherwise. It just seems that the system
> is sluggish.
> 
> I am using the new ReiserFS filesystem and I do know its still in heavy
> development perhaps my latency is due to this (?)

Reiserfs uses much more complex data structures then ext2 (trees..). I don't
think that latency has ever been a design criteria and all of the benchmarks
they use are pretty much pure throughput tests.

So it wouldn't be really surprising if reiserfs had very bad latency. You
should apply the timepegs patch and profile your kernel latency to see where
it's coming from.
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Re: Kernel 2.4.x and 2.4.1-preX - Higher latency then 2.2.x kernels?

[Shawn Starr]

Where can i get the patch?

I can apply it right now.

Gregory Maxwell wrote:

> On Sat, Jan 20, 2001 at 02:50:16PM -0500, Shawn Starr wrote:
> > It just seems that since using 2.4 ive noticed my poor Pentium 200Mhz
> > slow down whether being in X or otherwise. It just seems that the system
> > is sluggish.
> >
> > I am using the new ReiserFS filesystem and I do know its still in heavy
> > development perhaps my latency is due to this (?)
>
> Reiserfs uses much more complex data structures then ext2 (trees..). I don't
> think that latency has ever been a design criteria and all of the benchmarks
> they use are pretty much pure throughput tests.
>
> So it wouldn't be really surprising if reiserfs had very bad latency. You
> should apply the timepegs patch and profile your kernel latency to see where
> it's coming from.
> -
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Re: Kernel 2.4.x and 2.4.1-preX - Higher latency then 2.2.x kernels?

[Chris Mason]

On Saturday, January 20, 2001 02:59:24 PM -0500 Gregory Maxwell
<greg@linuxpower.cx> wrote:

> On Sat, Jan 20, 2001 at 02:50:16PM -0500, Shawn Starr wrote: 
>> It just seems that since using 2.4 ive noticed my poor Pentium 200Mhz
>> slow down whether being in X or otherwise. It just seems that the system
>> is sluggish.
>> 
>> I am using the new ReiserFS filesystem and I do know its still in heavy
>> development perhaps my latency is due to this (?)
> 
> Reiserfs uses much more complex data structures then ext2 (trees..). I
> don't think that latency has ever been a design criteria and all of the
> benchmarks they use are pretty much pure throughput tests.
> 
> So it wouldn't be really surprising if reiserfs had very bad latency. You
> should apply the timepegs patch and profile your kernel latency to see
> where it's coming from.

I'm actually very interested in fixing any latency problems.  If you do
these tests, please send the results along.

-chris
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Re: Kernel 2.4.x and 2.4.1-preX - Higher latency then 2.2.xkernels?

[Shawn Starr]

Sure, but Im not sure what to test ;)
If you've got any special patches for 2.4 lemme know and I'll apply them I've
got all night heh

Shawn.

Chris Mason wrote:

> On Saturday, January 20, 2001 02:59:24 PM -0500 Gregory Maxwell
> <greg@linuxpower.cx> wrote:
>
> > On Sat, Jan 20, 2001 at 02:50:16PM -0500, Shawn Starr wrote:
> >> It just seems that since using 2.4 ive noticed my poor Pentium 200Mhz
> >> slow down whether being in X or otherwise. It just seems that the system
> >> is sluggish.
> >>
> >> I am using the new ReiserFS filesystem and I do know its still in heavy
> >> development perhaps my latency is due to this (?)
> >
> > Reiserfs uses much more complex data structures then ext2 (trees..). I
> > don't think that latency has ever been a design criteria and all of the
> > benchmarks they use are pretty much pure throughput tests.
> >
> > So it wouldn't be really surprising if reiserfs had very bad latency. You
> > should apply the timepegs patch and profile your kernel latency to see
> > where it's coming from.
>
> I'm actually very interested in fixing any latency problems.  If you do
> these tests, please send the results along.
>
> -chris
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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Re: Kernel 2.4.x and 2.4.1-preX - Higher latency then 2.2.xkernels?

[Shawn Starr]

Applying now.

Andrew Morton wrote:

> Shawn,
>
> I've pretty much completed the low-latency patch against reiserfs.
> It seems to be a little more latency-prone than ext2, but under normal
> workloads it's not significant.  The worst-case is 100 milliseconds,
> but that's when you're doing insane things to it.
>
> You may care to apply http://www.uow.edu.au/~andrewm/linux/2.4.1-pre10-low-latency.patch
> against 2.4.1-pre10 and see if it "feels" different.  I'd be surprised
> if it does, but the result would be interresting.
>
> Note that the low-latency capability must be enabled under the
> "Processor type and features" menu, and if you also enable the
> low-latency sysctl option, you'll need to
>
>         echo 1 > /proc/sys/kernel/lowlatency
>
> to make it happen.  Creature feep :)
>
> Shawn Starr wrote:
> >
> > Sure, but Im not sure what to test ;)
> > If you've got any special patches for 2.4 lemme know and I'll apply them I've
> > got all night heh
> >
> > Shawn.
> >
> > Chris Mason wrote:
> >
> > > On Saturday, January 20, 2001 02:59:24 PM -0500 Gregory Maxwell
> > > <greg@linuxpower.cx> wrote:
> > >
> > > > On Sat, Jan 20, 2001 at 02:50:16PM -0500, Shawn Starr wrote:
> > > >> It just seems that since using 2.4 ive noticed my poor Pentium 200Mhz
> > > >> slow down whether being in X or otherwise. It just seems that the system
> > > >> is sluggish.
> > > >>
> > > >> I am using the new ReiserFS filesystem and I do know its still in heavy
> > > >> development perhaps my latency is due to this (?)
> > > >
> > > > Reiserfs uses much more complex data structures then ext2 (trees..). I
> > > > don't think that latency has ever been a design criteria and all of the
> > > > benchmarks they use are pretty much pure throughput tests.
> > > >
> > > > So it wouldn't be really surprising if reiserfs had very bad latency. You
> > > > should apply the timepegs patch and profile your kernel latency to see
> > > > where it's coming from.
> > >
> > > I'm actually very interested in fixing any latency problems.  If you do
> > > these tests, please send the results along.
> > >
> > > -chris
> > > -
> > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > > the body of a message to majordomo@vger.kernel.org
> > > Please read the FAQ at http://www.tux.org/lkml/
> >
> > -
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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Re: Kernel 2.4.x and 2.4.1-preX - Higher latency then 2.2.xkernels?

[Andrew Morton]

Shawn,

I've pretty much completed the low-latency patch against reiserfs.
It seems to be a little more latency-prone than ext2, but under normal
workloads it's not significant.  The worst-case is 100 milliseconds,
but that's when you're doing insane things to it.

You may care to apply http://www.uow.edu.au/~andrewm/linux/2.4.1-pre10-low-latency.patch
against 2.4.1-pre10 and see if it "feels" different.  I'd be surprised
if it does, but the result would be interresting.

Note that the low-latency capability must be enabled under the
"Processor type and features" menu, and if you also enable the
low-latency sysctl option, you'll need to

	echo 1 > /proc/sys/kernel/lowlatency

to make it happen.  Creature feep :)


Shawn Starr wrote:
> 
> Sure, but Im not sure what to test ;)
> If you've got any special patches for 2.4 lemme know and I'll apply them I've
> got all night heh
> 
> Shawn.
> 
> Chris Mason wrote:
> 
> > On Saturday, January 20, 2001 02:59:24 PM -0500 Gregory Maxwell
> > <greg@linuxpower.cx> wrote:
> >
> > > On Sat, Jan 20, 2001 at 02:50:16PM -0500, Shawn Starr wrote:
> > >> It just seems that since using 2.4 ive noticed my poor Pentium 200Mhz
> > >> slow down whether being in X or otherwise. It just seems that the system
> > >> is sluggish.
> > >>
> > >> I am using the new ReiserFS filesystem and I do know its still in heavy
> > >> development perhaps my latency is due to this (?)
> > >
> > > Reiserfs uses much more complex data structures then ext2 (trees..). I
> > > don't think that latency has ever been a design criteria and all of the
> > > benchmarks they use are pretty much pure throughput tests.
> > >
> > > So it wouldn't be really surprising if reiserfs had very bad latency. You
> > > should apply the timepegs patch and profile your kernel latency to see
> > > where it's coming from.
> >
> > I'm actually very interested in fixing any latency problems.  If you do
> > these tests, please send the results along.
> >
> > -chris
> > -
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@vger.kernel.org
> > Please read the FAQ at http://www.tux.org/lkml/
> 
> -
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Re: Kernel 2.4.x and 2.4.1-preX - Higher latency then 2.2.xkernels?

[Shawn Starr]

Andrew, the patch HAS made a difference. For example, while untaring glibc-2.2.1.tar.gz the
system was not sluggish (mouse movements in X) etc.

Seems to be a go for latency improvements on this system.

Shawn Starr wrote:

> Applying now.
>
> Andrew Morton wrote:
>
> > Shawn,
> >
> > I've pretty much completed the low-latency patch against reiserfs.
> > It seems to be a little more latency-prone than ext2, but under normal
> > workloads it's not significant.  The worst-case is 100 milliseconds,
> > but that's when you're doing insane things to it.
> >
> > You may care to apply http://www.uow.edu.au/~andrewm/linux/2.4.1-pre10-low-latency.patch
> > against 2.4.1-pre10 and see if it "feels" different.  I'd be surprised
> > if it does, but the result would be interresting.
> >
> > Note that the low-latency capability must be enabled under the
> > "Processor type and features" menu, and if you also enable the
> > low-latency sysctl option, you'll need to
> >
> >         echo 1 > /proc/sys/kernel/lowlatency
> >
> > to make it happen.  Creature feep :)

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Re: Kernel 2.4.x and 2.4.1-preX - Higher latency then 2.2.xkernels?

[Andrew Morton]

Shawn Starr wrote:
> 
> Andrew, the patch HAS made a difference. For example, while untaring glibc-2.2.1.tar.gz the
> system was not sluggish (mouse movements in X) etc.
> 
> Seems to be a go for latency improvements on this system.

hmm..  OK, thanks.

Chris, this seems to be a worthwhile improvement to mainstream
reiserfs, independent of the low-latency thing.   You can
probably achieve 10 milliseconds with just a few lines of
code - a subset of the patch which Shawn tested. (Unless you
were planning on magical algorithmic improvements...).

I'm all set up to generate those few lines of code, so
I'll propose a patch later this week.

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Re: Kernel 2.4.x and 2.4.1-preX - Higher latency then 2.2.xkernels?

[Shawn Starr]

It should also be noted, that while using GCC and other tasks, the latency has returned to 2.2
levels from my point. Before. If you want to me to do any testing I can do that.

I applied the timepegs patch:

Kernel timepegs enabled. See http://www.uow.edu.au/~andrewm/linux/

Shawn.

> >
> > Andrew, the patch HAS made a difference. For example, while untaring glibc-2.2.1.tar.gz the
> > system was not sluggish (mouse movements in X) etc.
> >
> > Seems to be a go for latency improvements on this system.
>
> hmm..  OK, thanks.
>
> Chris, this seems to be a worthwhile improvement to mainstream
> reiserfs, independent of the low-latency thing.   You can
> probably achieve 10 milliseconds with just a few lines of
> code - a subset of the patch which Shawn tested. (Unless you
> were planning on magical algorithmic improvements...).
>
> I'm all set up to generate those few lines of code, so
> I'll propose a patch later this week.
>
> -

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Re: Kernel 2.4.x and 2.4.1-preX - Higher latency then 2.2.xkernels?

[Andrew Morton]

Shawn Starr wrote:
> 
> Andrew, the patch HAS made a difference. For example, while untaring glibc-2.2.1.tar.gz the
> system was not sluggish (mouse movements in X) etc.
> 
> Seems to be a go for latency improvements on this system.

Shawn,

could you please try this patch in a pristine 2.4.1-pre10? It
gets reiserfs down to 4 milliseconds worst case.  If the
system's interactivity is still sluggish with this then
reiserfs isn't the cause.


Thanks.

--- linux-2.4.1-pre10/include/linux/reiserfs_fs.h	Tue Jan 23 19:28:16 2001
+++ linux-akpm/include/linux/reiserfs_fs.h	Sun Jan 28 22:37:11 2001
@@ -1161,7 +1161,8 @@
 #define fs_generation(s) ((s)->u.reiserfs_sb.s_generation_counter)
 #define get_generation(s) atomic_read (&fs_generation(s))
 #define FILESYSTEM_CHANGED_TB(tb)  (get_generation((tb)->tb_sb) != (tb)->fs_gen)
-#define fs_changed(gen,s) (gen != get_generation (s))
+#define __fs_changed(gen,s) (gen != get_generation (s))
+#define fs_changed(gen,s) ({if (current->need_resched) schedule(); __fs_changed(gen,s);})
 
 
 /***************************************************************************/
--- linux-2.4.1-pre10/fs/reiserfs/journal.c	Tue Jan 23 19:28:15 2001
+++ linux-akpm/fs/reiserfs/journal.c	Sun Jan 28 22:31:12 2001
@@ -2649,6 +2649,8 @@
       }
 #endif
       wait_on_buffer(bh) ;
+      if (current->need_resched)
+	schedule();
     }
     retry_count++ ;
   }
@@ -3085,6 +3087,8 @@
     /* copy all the real blocks into log area.  dirty log blocks */
     if (test_bit(BH_JDirty, &cn->bh->b_state)) {
       struct buffer_head *tmp_bh ;
+      if (current->need_resched)
+        schedule();
       tmp_bh = getblk(p_s_sb->s_dev, reiserfs_get_journal_block(p_s_sb) + 
 		     ((cur_write_start + jindex) % JOURNAL_BLOCK_COUNT), 
 				       p_s_sb->s_blocksize) ;
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Re: Kernel 2.4.x and 2.4.1-preX - Higher latency then 2.2.xkernels?

[Chris Mason]

On Sunday, January 28, 2001 02:29:09 PM +1100 Andrew Morton
<andrewm@uow.edu.au> wrote:

> Shawn Starr wrote:
>> 
>> Andrew, the patch HAS made a difference. For example, while untaring
>> glibc-2.2.1.tar.gz the system was not sluggish (mouse movements in X)
>> etc.
>> 
>> Seems to be a go for latency improvements on this system.
> 
> hmm..  OK, thanks.
> 
> Chris, this seems to be a worthwhile improvement to mainstream
> reiserfs, independent of the low-latency thing.   You can
> probably achieve 10 milliseconds with just a few lines of
> code - a subset of the patch which Shawn tested. (Unless you
> were planning on magical algorithmic improvements...).
> 
> I'm all set up to generate those few lines of code, so
> I'll propose a patch later this week.

Perfect, I was thinking exactly the same thing.  We have to be careful here
though, since the extra schedules will increase the chance the searching
has to be redone from scratch, which can have big performance ramifications.

I think your change to search_by_key will be the safest for performance
considerations, along with the change to prepare_for_delete_or_cut.  If
those won't be enough, we can attack reiserfs_get_block (who is probably
the biggest single offender without your patch).

-chris

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Re: Kernel 2.4.x and 2.4.1-preX - Higher latency then 2.2.xkernels?

[Shawn Starr]

Will this patch work with the low-latency patch? I have a few other patches in this kernel (one
fixing the ps hang issue).

Andrew Morton wrote:

> Shawn Starr wrote:
> >
> > Andrew, the patch HAS made a difference. For example, while untaring glibc-2.2.1.tar.gz the
> > system was not sluggish (mouse movements in X) etc.
> >
> > Seems to be a go for latency improvements on this system.
>
> Shawn,
>
> could you please try this patch in a pristine 2.4.1-pre10? It
> gets reiserfs down to 4 milliseconds worst case.  If the
> system's interactivity is still sluggish with this then
> reiserfs isn't the cause.
>
> Thanks.
>
> --- linux-2.4.1-pre10/include/linux/reiserfs_fs.h       Tue Jan 23 19:28:16 2001
> +++ linux-akpm/include/linux/reiserfs_fs.h      Sun Jan 28 22:37:11 2001
> @@ -1161,7 +1161,8 @@
>  #define fs_generation(s) ((s)->u.reiserfs_sb.s_generation_counter)
>  #define get_generation(s) atomic_read (&fs_generation(s))
>  #define FILESYSTEM_CHANGED_TB(tb)  (get_generation((tb)->tb_sb) != (tb)->fs_gen)
> -#define fs_changed(gen,s) (gen != get_generation (s))
> +#define __fs_changed(gen,s) (gen != get_generation (s))
> +#define fs_changed(gen,s) ({if (current->need_resched) schedule(); __fs_changed(gen,s);})
>
>
>  /***************************************************************************/
> --- linux-2.4.1-pre10/fs/reiserfs/journal.c     Tue Jan 23 19:28:15 2001
> +++ linux-akpm/fs/reiserfs/journal.c    Sun Jan 28 22:31:12 2001
> @@ -2649,6 +2649,8 @@
>        }
>  #endif
>        wait_on_buffer(bh) ;
> +      if (current->need_resched)
> +       schedule();
>      }
>      retry_count++ ;
>    }
> @@ -3085,6 +3087,8 @@
>      /* copy all the real blocks into log area.  dirty log blocks */
>      if (test_bit(BH_JDirty, &cn->bh->b_state)) {
>        struct buffer_head *tmp_bh ;
> +      if (current->need_resched)
> +        schedule();
>        tmp_bh = getblk(p_s_sb->s_dev, reiserfs_get_journal_block(p_s_sb) +
>                      ((cur_write_start + jindex) % JOURNAL_BLOCK_COUNT),
>                                        p_s_sb->s_blocksize) ;
> -
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Re: Kernel 2.4.x and 2.4.1-preX - Higher latency then 2.2.xkernels?

[Shawn Starr]

>  Andrew Morton
> <andrewm@uow.edu.au> wrote:

Ok, I've backed out of the low-latency patch but kept the timepegs patch in.
I've applied your reiserfs low-latency patch on a stock 2.4.1-pre11 kernel.

Let's see what happens :)

Shawn.



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