Priority inversion when using MTD

Priority inversion when using MTD

[Sekhar Nori]

Hi,

I have a high priority SCHED_FIFO task which runs out of a squashfs file system.
When this process needs to fetch a page from the flash (due to demand paging),
it is sometimes made to wait for another low priority SCHED_NORMAL
task which is doing an erase on some other mtd partition.

This helps other middle priority processes have a free run causing a
priority inversion issue.

The get_chip function in cfi_cmdset_0001.c uses a per chip wait queue
for all processes which need to wait for chip access.

Is there any way to avoid this scenario? Any help/pointers would be appreciated.

Thanks,
Sekhar Nori.

Re: Priority inversion when using MTD

[David Woodhouse]

On Thu, 2007-05-17 at 18:50 +0530, Sekhar Nori wrote:
> I have a high priority SCHED_FIFO task which runs out of a squashfs file system.
> When this process needs to fetch a page from the flash (due to demand paging),
> it is sometimes made to wait for another low priority SCHED_NORMAL
> task which is doing an erase on some other mtd partition.
 ...
> Is there any way to avoid this scenario? Any help/pointers would be appreciated.

mlockall(2)

-- 
dwmw2

Re: Priority inversion when using MTD

[Sekhar Nori]

On 5/17/07, David Woodhouse <dwmw2@infradead.org> wrote:
> On Thu, 2007-05-17 at 18:50 +0530, Sekhar Nori wrote:
> > I have a high priority SCHED_FIFO task which runs out of a squashfs file system.
> > When this process needs to fetch a page from the flash (due to demand paging),
> > it is sometimes made to wait for another low priority SCHED_NORMAL
> > task which is doing an erase on some other mtd partition.
>  ...
> > Is there any way to avoid this scenario? Any help/pointers would be appreciated.
>
> mlockall(2)

But doing so for all SCHED_FIFO tasks would make the system run out of memory :(

-
Sekhar Nori