linux-kernel - Re: init's children list is long and slows reaping children.

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Message-ID: <64bb37e0704092309v49ae1ddbvb22e3f213ccab28e@mail.gmail.com>
Date:	Tue, 10 Apr 2007 08:09:55 +0200
From:	"Torsten Kaiser" <just.for.lkml@...glemail.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	"Dave Jones" <davej@...hat.com>, "Jeff Garzik" <jeff@...zik.org>,
	"Robin Holt" <holt@....com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	"Jack Steiner" <steiner@...ricas.sgi.com>
Subject: Re: init's children list is long and slows reaping children.

On 4/10/07, Andrew Morton <akpm@...ux-foundation.org> wrote:
> : root       299  0.0  0.0      0     0 ?        S    18:51   0:00 [scsi_eh_0]
> : root       300  0.0  0.0      0     0 ?        S    18:51   0:00 [scsi_eh_1]
> : root       305  0.0  0.0      0     0 ?        S    18:51   0:00 [scsi_eh_2]
> : root       306  0.0  0.0      0     0 ?        S    18:51   0:00 [scsi_eh_3]
>
> This machine has one CPU, one sata disk and one DVD drive.  The above is
> hard to explain.

One thread per port, not per device.

  796 ?        S      0:00  \_ [scsi_eh_0]
  797 ?        S      0:00  \_ [scsi_eh_1]
  798 ?        S      0:00  \_ [scsi_eh_2]
  819 ?        S      0:00  \_ [scsi_eh_3]
  820 ?        S      0:00  \_ [scsi_eh_4]
  824 ?        S      0:00  \_ [scsi_eh_5]
  825 ?        S      0:14  \_ [scsi_eh_6]

bardioc ~ # lsscsi -d
[0:0:0:0]    disk    ATA      ST3160827AS      3.42  /dev/sda[8:0]
[1:0:0:0]    disk    ATA      ST3160827AS      3.42  /dev/sdb[8:16]
[5:0:0:0]    disk    ATA      IBM-DHEA-36480   HE8O  /dev/sdc[8:32]
[5:0:1:0]    disk    ATA      Maxtor 6L160P0   BAH4  /dev/sdd[8:48]
[6:0:0:0]    cd/dvd  HL-DT-ST DVDRAM GSA-4081B A100  /dev/sr0[11:0]
bardioc ~ # lsscsi -H
[0]    sata_promise
[1]    sata_promise
[2]    sata_promise
[3]    sata_via
[4]    sata_via
[5]    pata_via
[6]    pata_via

The bad is, that there is always a thread, even if the hardware is not
even hotplug capable.
Don't know if the thread is even needed for hotplug...

> I don't think it's completely silly to object to all this.  Sure, a kernel
> thread is worth 4k in the best case, but I bet they have associated unused
> resources and as we've seen, they can cause overhead.

For me its not the 4k that annoy me, but the clutter in ps or top.

Torsten
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