Re: [PATCH 34/35] async: use workqueue for worker pool

From: Arjan van de Ven
Date: Tue Jun 29 2010 - 14:07:26 EST

On 6/29/2010 9:59 AM, Tejun Heo wrote:
Hello, Arjan.

On 06/29/2010 06:40 PM, Arjan van de Ven wrote:
uh? clearly the assumption is that if I have a 16 CPU machine, and 12
items of work get scheduled,
that we get all 12 running in parallel. All the smarts of cmwq surely
only kick in once you've reached the
"one work item per cpu" threshold ???
Hmmm... workqueue workers are bound to certain cpu, so if you schedule
a work on a specific CPU, it will run there. Once a cpu gets
saturated, the issuing thread will be moved elsewhere. I don't think
it matters to any of the current async users one way or the other,
would it?

we might be talking past eachother. ;-)

let me define an example that is simple so that we can get on the same page

assume a system with "enough" cpus, say 32.
lets say we have 2 async tasks, that each do an mdelay(1000); (yes I know stupid, but exagerating things makes things easier to talk about)
lets also assume that they get scheduled right back to back from the same code on the same cpu.

will the end result be that the first mdelay() task complete before the second one gets started, or will the end result be that
the 2nd one will notice the first cpu is busy, and find a second cpu to run in parallel with.

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