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

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 (?)

Quoted 6 lines · Shawn Starr

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.

Quoted 8 lines · On Saturday, January 20, 2001 02:59:24 PM -0500 Gregory Maxwell…

Quoted 6 lines · Shawn Starr

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 (?)

Quoted 7 lines

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.

(quoted diff) +0 -2

-chris
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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.

Quoted 22 lines · Chris Mason

Quoted 8 lines · On Saturday, January 20, 2001 02:59:24 PM -0500 Gregory Maxwell…

Quoted 6 lines · Shawn Starr

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 (?)

Quoted 7 lines

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.

Quoted 5 lines

(quoted diff) +0 -2

-chris
-

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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 :)

Quoted 41 lines · 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.

Quoted 24 lines · Chris Mason

Quoted 8 lines · On Saturday, January 20, 2001 02:59:24 PM -0500 Gregory Maxwell…

Quoted 6 lines · Shawn Starr

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 (?)

Quoted 7 lines

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.

(quoted diff) +0 -2

-chris
-

Quoted 3 lines

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Applying now.

Quoted 18 lines · 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 :)

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.

Quoted 6 lines · 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.

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.

Andrew Morton
<[email protected]> wrote:

Quoted 5 lines

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.

-

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.

Quoted 5 lines · 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,

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.

include/linux/reiserfs_fs.h Sun Jan 28 22:37:11 2001 renamed from include/linux/reiserfs_fs.h Tue Jan 23 19:28:16 2001 +2 -1

@@ -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);})
 
 
 /***************************************************************************/

fs/reiserfs/journal.c Sun Jan 28 22:31:12 2001 renamed from fs/reiserfs/journal.c Tue Jan 23 19:28:15 2001 +4 -1

@@ -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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Quoted 6 lines · Shawn Starr

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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