Re: raid6check extremely slow ?

[Piergiorgio Sartor <piergiorgio.sartor@nexgo.de>]

On Mon, May 11, 2020 at 10:53:05PM +0200, Giuseppe Bilotta wrote:
> Hello Piergiorgio,
> 
> On Mon, May 11, 2020 at 6:15 PM Piergiorgio Sartor
> <piergiorgio.sartor@nexgo.de> wrote:
> > Hi again!
> >
> > I made a quick test.
> > I disabled the lock / unlock in raid6check.
> >
> > With lock / unlock, I get around 1.2MB/sec
> > per device component, with ~13% CPU load.
> > Wihtout lock / unlock, I get around 15.5MB/sec
> > per device component, with ~30% CPU load.
> >
> > So, it seems the lock / unlock mechanism is
> > quite expensive.
> >
> > I'm not sure what's the best solution, since
> > we still need to avoid race conditions.
> >
> > Any suggestion is welcome!
> 
> Would it be possible/effective to lock multiple stripes at once? Lock,
> say, 8 or 16 stripes, process them, unlock. I'm not familiar with the
> internals, but if locking is O(1) on the number of stripes (at least
> if they are consecutive), this would help reduce (potentially by a
> factor of 8 or 16) the costs of the locks/unlocks at the expense of
> longer locks and their influence on external I/O.

Probabily possible, from the technical
point of view, even if I do not know
either the effect.

From the coding point of view, a bit
tricky, boundary conditions and so on
must be properly considered.

> 
> --
> Giuseppe "Oblomov" Bilotta

-- 

piergiorgio