[lkml]   [2009]   [May]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 2/2] UBIFS: start using hrtimers
Peter Zijlstra wrote:
> On Fri, 2009-05-29 at 18:09 +0300, Artem Bityutskiy wrote:
>> From: Artem Bityutskiy <>
>> Subject: [PATCH 2/2] UBIFS: start using hrtimers
>> UBIFS uses timers for write-buffer write-back. It is not
>> crucial for us to write-back exactly on time. We are fine
>> to write-back a little earlier or later. And this means
>> we may optimize UBIFS timer so that it could be groped
>> with a close timer event, so that the CPU would not be
>> waken up just to do the write back. This is optimization
>> to lessen power consumption, which is important in
>> embedded devices UBIFS is used for.
>> hrtimers have a nice feature: they are effectively range
>> timers, and we may defind the soft and hard limits for
>> it. Standard timers do not have these feature. They may
>> only be made deferrable, but this means there is effectively
>> no hard limit. So, we will better use hrtimers.
>> Signed-off-by: Artem Bityutskiy <>
>> ---
> Seems sane enough from a hrtimer POV, but isn't this already
> functionality that the VFS/pdflush provide?

Yeah, VFS/pdflush takes care of the page-cache and inode cache,
and dirty superblocks. But additionally to this UBIFS has its
own small buffer of (usually) 2KiB size, we call it write-buffer.
This is a very important optimization for NAND flash. And we
have a separate timer to synchronize this small write-buffer.

I was also thinking to hook to VFS, which would mean creating
a fake inode representing our write-bufffer. But this would be
very hacky.

Best Regards,
Artem Bityutskiy (Артём Битюцкий)
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2009-05-29 16:01    [from the cache]
©2003-2014 Jasper Spaans. hosted at Digital Ocean