Date: Wed, 22 May 2013 13:48:00 +0000 From: Orit Moskovich <oritm@mellanox.com> To: John Baldwin <jhb@freebsd.org> Cc: "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: RE: FreeBSD spinlock - compatibility layer Message-ID: <981733489AB3BD4DB24B48340F53E0A55B0D3CD8@MTLDAG01.mtl.com> In-Reply-To: <201305220859.32948.jhb@freebsd.org> References: <981733489AB3BD4DB24B48340F53E0A55B0CFD79@MTLDAG01.mtl.com> <201305211220.16776.jhb@freebsd.org> <981733489AB3BD4DB24B48340F53E0A55B0D39EF@MTLDAG01.mtl.com> <201305220859.32948.jhb@freebsd.org>
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>From the mutex man page " By default, MTX_DEF mutexes will context switch w= hen they are already held." How is sleeping forbidden, but blocking on a mutex that might context switc= h is ok? -----Original Message----- From: John Baldwin [mailto:jhb@freebsd.org]=20 Sent: Wednesday, May 22, 2013 04:06 PM To: Orit Moskovich Cc: freebsd-arch@freebsd.org Subject: Re: FreeBSD spinlock - compatibility layer On Wednesday, May 22, 2013 2:14:51 am Orit Moskovich wrote: > From what I've read in "FreeBSD - device drivers" book by Joseph Kong=20 > on interrupt handling, you cannot voluntarily context switch (that is, sleep) = in interrupt threads . That is not the same thing. By sleep it means call a *sleep() function or = wait on a cond var. Not block on a mutex or rwlock. > In any case, I think that the functionality of spin mutex should=20 > remain as is, and not modified to sleep mutex, as it can be used in places that sleep= mustn't be used, or that require the properties of the spin due to perform= ance considerations. No, spin locks are _slower_ and reduce performance. FreeBSD is much more l= ike Solaris in this regard. Spin mutexes on FreeBSD are similar to dispatc= her locks in Solaris which 99% of the kernel should never use. -- John Baldwin
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