[vdr] [seems to be solved] sync problems (was: too many processes?)

Udo Richter udo_richter at gmx.de
Wed Dec 14 17:20:21 CET 2005


André Bischof wrote:
> as I wrote I was investigating in sync problems I experienced.
> 
> I haven't tested it thoroughly, but on a first glance it looks like
> adding the kernel parameter "elevator=cfq" to grub's menu.lst to run
> another scheduler solves the problem (this was suggested on
> vdr-portal.de). Thus
> 
> kernel          /boot/vmlinuz-2.6.12-1-386 root=/dev/hda1 ro vga=0x31A
> elevator=cfq
> 
> did it for me.

I had some thoughts about that too.
AFAIK the CFQ scheduler shares I/O access equally across all processes, 
and is mainly targeted to multi-user environments. If only one process 
is doing all the I/O, it shouldn't be that effective.

For kernel 2.4, there is no CFQ, so lets ignore 2.4. For most kernel 
2.6, the kernel and/or the libc understands native threads, and vdr runs 
in a single process, so CFQ shouldn't be useful, should it?
(even if vdr runs without NPTL, linuxthreads joins the threads into one pid)

However, based on your posted logs, your kernel and glibc seems to use 
linuxthreads with thread emulation using processes, so it may have an 
effect for you.

Cheers,

Udo



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