Date: Tue, 28 Nov 2006 16:31:18 -0500 From: John Baldwin <jhb@freebsd.org> To: freebsd-arch@freebsd.org Cc: Poul-Henning Kamp <phk@phk.freebsd.dk> Subject: Re: a proposed callout API Message-ID: <200611281631.19224.jhb@freebsd.org> In-Reply-To: <7105.1163451221@critter.freebsd.dk> References: <7105.1163451221@critter.freebsd.dk>
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On Monday 13 November 2006 15:53, Poul-Henning Kamp wrote: > The proposed API > ---------------- > > tick_t XXX_ns_tick(unsigned nsec, unsigned *low, unsigned *high); > Caculate the tick value for a given timeout. > Optionally return theoretical lower and upper limits to > actual value, > > tick_t XXX_s_tick(unsigned seconds) > Caculate the tick value for a given timeout. > > The point behind these two functions is that we do not want to > incur a scaling operating at every arming of a callout. Very > few callouts use varying timeouts (and for those, no avoidance > is possible), but for the rest, precalculating the correct > (opaque) number is a good optimization. One note and one question. First, the note. I was planning on rototilling our sleep() APIs to 1) handle multiple locking primitives, and 2) use explicit timescales rather than hz. I had intended on using microseconds with a negative value indicating a relative timeout (so an 'uptime' timeout, i.e. trigger X us from now) and a positive value indicating an absolute timeout (time_t-ish, and subject to ntp changes). Partly because (IIRC) Windows does something similar (negative: relative, positive: absolute, and in microseconds too IIRC) and Darwin as well. Part of the idea was to fix places that abused tsleep(..., 1), etc. to figure out a "real" sleep interval. With your proposal, I would probably change the various sleep routines to take a tick_t instead. That leads me to my question if if you would want to support the notion of absolute vs relative timeouts? Also, my other API change I was going to do was something like this: msleep() -> mtx_sleep() msleep_spin() -> sl_sleep() (or some such, was talking with ups@ at BSDCan about divorcing spin locks from mutexes altogether, including a separate API namespace, since it's practically already separate as it is) new functions such as: rw_sleep(), sx_sleep() (ZFS wants this I think), but this is rather secondary. I'd just rather get the pain and suffering over all at once. -- John Baldwin
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