Re: [RFC PATCH]Multi-threaded Initcall with dependence support

[Dave Jones <davej@redhat.com>]

On Tue, May 29, 2007 at 09:47:53AM +0800, Yang Sheng wrote:
 > On Tuesday 29 May 2007 06:52, Randy Dunlap wrote:
 > > On Mon, 28 May 2007 15:03:10 +0800 Yang Sheng wrote:
 > > > Why we need this:
 > > >
 > > > It can speed up the calling of initcalls, especially useful for some
 > > > embed device.
 > >
 > > Can you give concrete example(s) of why we need this?
 > > Any real configs/hardware where it helps and how much it helps.
 > >
 > 
 > We didn't got the precise data at hand now, because we should build a complete  
 > stable initcall dependence relationship for it, but we can't do it now. 
 > 
 > But we have done a relative stable test in a common x86_64 machine, with 2 
 > threads and one dependence relation(pnpacpi_init depends on pnp_init and 
 > acpi_init). The result is the time spending on initcall calling reducing from 
 > about _5s_ to _2s_ (make the kernel with the defconfig). We analyzed the 
 > dmesg and found the most of time was save by run ide_generic_init and 
 > piix_init in parallel. 
 > 
 > Of course the dependence in the test case is not sufficient, but the effect is 
 > shown. 
 > 
 > We think this patch would be very useful in some embed deviced which requires 
 > fast boot speed. Some server may benefit too because of it's long time for 
 > device initiation. 

If we decide to do this, we should also introduce a way to disable it
at runtime with initcall=noparallel or something.  Why?
Because right now when people say "my computer hangs during bootup"
we can ask them to boot with initcall_debug and usually find out
the last thing it did before it locked up.   If we parallelise this,
the output will be a lot harder to decipher.

	Dave

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