Re: [DRIVER SUBMISSION] DRBD wants to go mainline

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Jul 25, 2007, at 22:03:37, [email protected] wrote:
On Wed, 25 Jul 2007, Satyam Sharma wrote:
On 7/25/07, Lars Ellenberg <[email protected]> wrote:
On Wed, Jul 25, 2007 at 04:41:53AM +0530, Satyam Sharma wrote:
[...]
But where does the "send" come into the picture over here -- a send won't block forever, so I don't foresee any issues whatsoever w.r.t. kthreads conversion for that. [ BTW I hope you're *not* using any signals-based interface for your kernel thread _at all_. Kthreads disallow (ignore) all signals by default, as they should, and you really shouldn't need to write any logic to handle or > do-certain-things-on-seeing a signal in a well designed kernel thread. ] and the sending latency is crucial to performance, while the recv will not timeout for the next few seconds. Again, I don't see what sending latency has to do with a kernel_thread to kthread conversion. Or with signals, for that matter. Anyway, as Kyle Moffett mentioned elsewhere, you could probably look at other examples (say cifs_demultiplexer_thread() in fs/cifs/connect.c).

the basic problem, and what we use signals for, is: it is waiting in recv, waiting for the peer to say something. but I want it to stop recv, and go send something "right now".

That's ... weird. Most (all?) communication between any two parties would follow a protocol where someone recv's stuff, does something with it, and sends it back ... what would you send "right now" if you didn't receive anything?

becouse even though you didn't receive anything you now have something important to send.

remember that both sides can be sitting in receive mode. this puts them both in a position to respond to the other if the other has something to say.

Why not just have 2 threads, one for "sending" and one for "receiving". When your receiving thread gets data it takes appropriate locks and processes it, then releases the locks and goes back to waiting for packets. Your sending thread would take appropriate locks, generate data to send, release locks, and transmit packets. You don't have to interrupt the receive thread to send packets, so where's the latency problem, exactly?

If I were writing that in userspace I would have:

(A) The pool of IO-generating threads (IE: What would ordinarily be userspace)
(B) One or a small number of data-reception threads.
(C) One or a small number of data-transmission threads.

When you get packets to process in your network-reception thread(s), you queue appropriate disk IOs and any appropriate responses with your transmission thread(s). You can basically just sit in a loop on tcp_recvmsg=>demultiplex=>do-stuff. When your IO-generators actually make stuff to send you queue such data for disk IO, then packetize it and hand it off to your data-transmission threads.

If you made all your sockets and inter-thread pipes nonblocking then in userspace you would just epoll_wait() on the sockets and pipes and be easily able to react to any IO from anywhere.

In kernel space there are similar nonblocking interfaces, although it would probably be easier just to use a couple threads.

Cheers,
Kyle Moffett

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux