Date: Wed, 5 Feb 2003 01:37:54 +0100 From: Brad Knowles <brad.knowles@skynet.be> To: phk@freebsd.org Cc: Brad Knowles <brad.knowles@skynet.be>, current@freebsd.org Subject: Re: Preview: GEOMs statistics code. Message-ID: <a05200f0dba6606ca5385@[146.106.12.76]> In-Reply-To: <27759.1044403667@critter.freebsd.dk> References: <27759.1044403667@critter.freebsd.dk>
next in thread | previous in thread | raw e-mail | index | archive | help
At 1:07 AM +0100 2003/02/05, phk@freebsd.org wrote:
> I don't have a queue-depth as such, but I have number of transactions
> in transit. Will a snapshot of that at the time of the read do
> what you want ? I am too sleepy to know if that will allow you to
> calculate the average number of outstanding requests precisely.
I would think that should do just fine. So long as we can get
some sense of %busy (and %wait) as well as average service times
(over the sample period), that should let us fill out those last
columns in `iostat -x`.
> I won't be locking the stats counters, so reads may get inconsistent
> results.
>
> There is no risk for the updates, because all the updating happens in
> the g_up thread, so there is no contention for changing the kernel
> fields.
>
> The risk is that the copy passed to userland may happen in the
> middle of an update and therefore have a field with a weird value
> which will look OK at the next reading.
>
> The risk is quite small because the g_up thread has higher priority than
> anything coming in from userland will ever have.
This is the same kind of risk that we have with `ps`, right? In
that the data is in the process of changing as we are reading it, so
you can't always take the data it prints out too literally? IMO,
that's a perfectly fine limitation to live with, for the results that
it allows us to get.
--
Brad Knowles, <brad.knowles@skynet.be>
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety."
-Benjamin Franklin, Historical Review of Pennsylvania.
GCS/IT d+(-) s:+(++)>: a C++(+++)$ UMBSHI++++$ P+>++ L+ !E-(---) W+++(--) N+
!w--- O- M++ V PS++(+++) PE- Y+(++) PGP>+++ t+(+++) 5++(+++) X++(+++) R+(+++)
tv+(+++) b+(++++) DI+(++++) D+(++) G+(++++) e++>++++ h--- r---(+++)* z(+++)
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-current" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?a05200f0dba6606ca5385>