Low latency for recent kernels

2.4.18-pre3 with 2.4.17-low-latency.patch worked fine on this system 2.4.18-pre6 with 2.4.18-pre6-low-latency.patch panics at boot time. 2.4.18-pre6 is fine also.

System has reiserfs root filesystem. No modules. /usr/src/linux/System.map was the System.map for 2.4.18pre6ll for the ksymoops below.

No modules in ksyms, skipping objects
No ksyms, skipping lsmod

Kernel panic: can't allocate root vfsmount
 <1>Unable to handle kernel NULL pointer dereference at virtual address 0000002c
c01234d3
*pde = 00000000
Oops: 0000
CPU:    0
EIP:    0010:[<c01234d3>]    Not tainted

Using defaults from ksymoops -t elf32-i386 -a i386
EFLAGS: 00010046
eax: 00000000 ebx: 00000008 ecx: 00000000 edx: 00000073
esi: 00000000 edi: 00000018 ebp: 00000020 esp: c0215e78
ds: 0018 es: 0018 ss: 0018
Process . (pid: -1072541344, stackpage=c0215000)

Stack: 00000018 00000001 00000018 c0214568 c0117e6c 00000000 00000020 c0214000
       00000018 00000018 00000000 c0117f4c 00000018 00000001 c0214568 00000086
       00000018 c0214000 c0117ff4 00000018 00000001 c0214000 01ebb409 c0214000
Call Trace: [<c0117e6c>] [<c0117f4c>] [<c0117ff4>] [<c0118253>] [<c0117208>]
   [<c0117291>] [<c011759f>] [<c010a889>] [<c0107d1c>] [<c0107e82>] [<c0105000>]
   [<c0109c18>] [<c0105000>] [<c0112020>]
Code: f6 46 2c 01 74 02 0f 0b 9c 5f fa 8b 4e 08 39 d9 75 22 8b 4e

Trace; c0117e6c <send_signal+2c/f0>
Trace; c0117f4c <deliver_signal+1c/50>
Trace; c0117ff4 <send_sig_info+74/88>
Trace; c0118252 <send_sig+1a/20>
Trace; c0117208 <update_one_process+68/d4>
Trace; c0117290 <update_process_times+1c/88>
Trace; c011759e <do_timer+22/70>
Trace; c010a888 <timer_interrupt+60/10c>
Trace; c0107d1c <handle_IRQ_event+30/5c>
Trace; c0107e82 <do_IRQ+6a/a8>
Trace; c0105000 <_stext+0/0>
Trace; c0109c18 <call_do_IRQ+6/e>
Trace; c0105000 <_stext+0/0>
Trace; c0112020 <panic+c0/d0>
Code; c01234d2 <kmem_cache_alloc+2a/b8>
00000000 <_EIP>:
Code; c01234d2 <kmem_cache_alloc+2a/b8> <=====
0: f6 46 2c 01 testb $0x1,0x2c(%esi) <=====
Code; c01234d6 <kmem_cache_alloc+2e/b8>
4: 74 02 je 8 <_EIP+0x8> c01234da <kmem_cache_alloc+32/b8>
Code; c01234d8 <kmem_cache_alloc+30/b8>
6: 0f 0b ud2a
Code; c01234da <kmem_cache_alloc+32/b8>
8: 9c pushf
Code; c01234da <kmem_cache_alloc+32/b8>
9: 5f pop %edi
Code; c01234dc <kmem_cache_alloc+34/b8>
a: fa cli
Code; c01234dc <kmem_cache_alloc+34/b8>
b: 8b 4e 08 mov 0x8(%esi),%ecx
Code; c01234e0 <kmem_cache_alloc+38/b8>
e: 39 d9 cmp %ebx,%ecx
Code; c01234e2 <kmem_cache_alloc+3a/b8>
10: 75 22 jne 34 <_EIP+0x34> c0123506 <kmem_cache_alloc+5e/b8>
Code; c01234e4 <kmem_cache_alloc+3c/b8>
12: 8b 4e 00 mov 0x0(%esi),%ecx

<0>Kernel panic: Aiee, killing interrupt handler!

Randy Hron

Ditto here -

2.4.18-pre6 + previous low latency patch boots & runs -

2.4.18-pre6 + latest low latency panics after this line:

Mount-cache hash table entries: 8192 (order: 4, 65536 bytes)

(next line would have been "Buffer-cache hash table entries...")

Here is the oops (be advised, it's copied by hand)

Kernel panic: can't allocate root vfsmount
<1>Unable to handle kernel NULL pointer dereference at virtual address 00000000c011a830
*pde = 00000000
Oops: 0000
CPU:    0
EIP:    0010:[<c011a830>]  Not tainted

Using defaults from ksymoops -t elf32-i386 -a i386
EFLAGS: 00010207
eax: 000001f3 ebx: 00000001 ecx: 00000000 edx: 00000000
esi: 00000000 edi: c02425a0 ebp: c020bf10 esp: c020bf10
ds: 0018 es: 0018 ss: 0018
Process (pid: -1072520631, stackpage=c020b000)

Stack: c020bf28 c011a8aa c020bf38 c024a5c0 00000000 c02425a0 c020bf30 c01178dd
      c020bf48 c01177ef 00000000 00000000 c02425c0 fffffff6 c020bf64 
c01175db
      c02425c0 00000046 c020bf84 00000000 c0240900 c020bf7c c01082ac 
c01f9bc8
Call Trace:  [<c011a8aa>] [<c01178dd>] [<c01177ef>] [<c01175db>] [<c01082ac>]
[<c0105000>] [<c0105000>] [<c0110018>] [<c0113382>]
Code: 8b 02 85 c0 74 07 8b 02 83 e0 02 74 06 81 c1 c0 08 00 00 8b

Trace; c011a8aa <timer_bh+4a/270>
Trace; c01178dd <bh_action+1d/50>
Trace; c01177ef <tasklet_hi_action+4f/70>
Trace; c01175db <do_softirq+5b/b0>
Trace; c01082ac <do_IRQ+ac/c0>
Trace; c0105000 <_stext+0/0>
Trace; c0105000 <_stext+0/0>
Trace; c0110018 <do_page_fault+28/555>
Trace; c0113382 <panic+e2/f0>
Code; c011a830 <count_active_tasks+20/50>
00000000 <_EIP>:

Code;  c011a830 <count_active_tasks+20/50>   <=====
  0:   8b 02                     mov    (%edx),%eax   <=====
Code;  c011a832 <count_active_tasks+22/50>
  2:   85 c0                     test   %eax,%eax
Code;  c011a834 <count_active_tasks+24/50>
  4:   74 07                     je     d <_EIP+0xd> c011a83d 
<count_active_tasks+2d/50>
Code;  c011a836 <count_active_tasks+26/50>
  6:   8b 02                     mov    (%edx),%eax
Code;  c011a838 <count_active_tasks+28/50>
  8:   83 e0 02                  and    $0x2,%eax
Code;  c011a83b <count_active_tasks+2b/50>
  b:   74 06                     je     13 <_EIP+0x13> c011a843 
<count_active_tasks+33/50>
Code;  c011a83d <count_active_tasks+2d/50>
  d:   81 c1 c0 08 00 00         add    $0x8c0,%ecx
Code;  c011a843 <count_active_tasks+33/50>
 13:   8b 00                     mov    (%eax),%eax

Kernel panic: Aiee, killing interrupt handler!

It looks like the newer version has substantial
changes in filemap.c and page_alloc.c relative
the the older version; if I had more time I'd
have looked into it further -

Best Regards,

joe

Yes, sorry about that. That patch had a completely untested, experimental and buggy chunk in it which kinda escaped from the factory.

I've uploaded a saner version.

-

Hi,

I'm sending some feedback !
:-)

I'm trying this patch... (in 2.4.18-pre6)
I'm feeling a improved performance ,as a desktop user. I'm working with KDE2, Netbeans and VMWare. Pentium III 666Mhz , 192M Ram, 10GB HD.

What are the tools to check this better performance? Or my impression is sufficient ?

Thanks

Mauricio

Is good. Thanks.

I'm a little surprised that desktop users do notice significant benefits with all the latency/preempt patches. If you actually instrument the kernel's behaviour, the stalls are in fact quite small and infrequent. See the histograms in

http://www.uwsg.iu.edu/hypermail/linux/kernel/0201.0/1624.html

Probably, poor interactivity on the desktop is more due to waiting on disk reads - a combination of bad read latency in the presence of write traffic and unfortunate page replacement decisions.

Try http://www.zipworld.com.au/~akpm/linux/2.4/2.4.18-pre6/read-latency2.patch

The simplest tool to use is Mark Hahn's `realfeel' app. See
http://www.zip.com.au/~akpm/linux/amlat.tar.gz

-

Yep, and half-formed ideas of process scheduling. The good news is, it's all being worked on by people who know what they're doing (including, obviously, you).

--
Daniel