Date: Thu, 31 May 2007 21:41:18 -0600 From: Scott Long <scottl@samsco.org> To: Hidetoshi Shimokawa <simokawa@freebsd.org> Cc: freebsd-scsi@freebsd.org Subject: Re: scsi_target with multiple luns Message-ID: <465F955E.7050103@samsco.org> In-Reply-To: <86tztspdil.wl%simokawa@FreeBSD.ORG> References: <86tztspdil.wl%simokawa@FreeBSD.ORG>
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Hidetoshi Shimokawa wrote: > I have not fully analyzed the problem but I'll describe it just for a note. > I'd like to ask maintainers of scsi_target for further analysis. > > I experiance a problem with small number(1) of simq and multiple > scsi_target(8) instances. > > As far as I understand, the following situation could occur under a fairly > heavy load. > > 1. process A send a request -> cam send to sim > 2. process B send a request -> blocked because the simq is full > 3. the request of process A is finished (in the context of process A) > 4. cam/scsi_target tries to send the request of process B. > But the mapped memory is of process A, and scsi_target send wrong > ccb to sim. > > Maybe, we should rewrite scsi_target in kernel space with GEOM support.. I'm unclear on how GEOM would fix this. Also, scsi targets aren't always DA devices. I dedicated scsi_da_target device that is backed by GEOM might be interesting, though. Even more interesting would be a direct DMA method that required no KVA mappings for the data. Scott
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