From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?iso-8859-1?Q?Jakob_=D8stergaard?= Subject: Re: Q: Priority of md_thread() Date: Wed, 22 May 2002 22:45:03 +0200 Sender: linux-raid-owner@vger.kernel.org Message-ID: <20020522224503.E586@unthought.net> References: <9CFB9DA5261CD611A29B00508B789048654302@ex-deu-munich02.force.de> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <9CFB9DA5261CD611A29B00508B789048654302@ex-deu-munich02.force.de>; from Kay.Potthoff@force.de on Wed, May 22, 2002 at 01:59:57PM +0200 To: "Potthoff, Kay" Cc: "Linux RAID Mailing List (E-mail)" List-Id: linux-raid.ids On Wed, May 22, 2002 at 01:59:57PM +0200, Potthoff, Kay wrote: > I have a question regarding the priority of the md_thread() function > (defined in md.c). >=20 > I have seen that the priority of this thread is set to -20 (parameter > current->nice), which means that this thread takes the highest priori= ty. The > problem I have is that this thread blocks some other task that is ans= wering > keep alive network pings from another (sibling) node. Because the kee= p alive > answers are blocked the other node decides to take-over the RAID. Thi= s > situation leeds to the fact that two nodes try to start the RAID. MD = don't > like this. The RAID is considered to be faulty and both nodes try to = repair > it, that is a problem. That system cannot be stable. Remember the -20 is only for the CPU scheduler, and the md_thread is no= t CPU bound (unless you have ISA controllers, or *very* special disks). What= I am trying to say is, I doubt much would change if the nice level was chang= ed to 20 instead... I think your problem is that something (and probably as you state, md_t= hread) is causing fluctuations in the ping replies, causing your other nodes t= o take an action which they shouldn't take based on a ping fluctuation (that c= ould just as easily be caused by a packet loss or some other random event in= the whole computer-network-computer system). If you want multiple nodes mounting the same array, you need some consi= stency protocol to be able to *guarantee* that no two nodes will try to master= the same array simultaneously. Ping fluctuations do not constitute a consis= tency protocol. > I figuered out that the cause of this problem is the high priority of= the > md_thread() function. I feel tempted to decrease this priority, but I= feel > some upcoming ache in my belly because I don't know the exact reason = why the > priority had been set to -20. I hope that somebody can explain me why= ! The > comments in the sources seem to regard to RAID-5 personality. If so t= hat > would be no problem, I intend only to use RAID-1. Please let me know if I completely misunderstood the situation :) --=20 =2E............................................................... : jakob@unthought.net : And I see the elder races, : :.........................: putrid forms of man : : Jakob =D8stergaard : See him rise and claim the earth, : : OZ9ABN : his downfall is at hand. : :.........................:............{Konkhra}...............: - To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html