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Re: [Xen-devel] QLogic Fibre Channel HBA Support

To: Steve Traugott <stevegt@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] QLogic Fibre Channel HBA Support
From: Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>
Date: Tue, 06 Jul 2004 08:26:43 +0100
Cc: Brian Wolfe <brianw@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxxx, Ian.Pratt@xxxxxxxxxxxx
Delivery-date: Tue, 06 Jul 2004 08:27:51 +0100
Envelope-to: steven.hand@xxxxxxxxxxxx
In-reply-to: Your message of "Mon, 05 Jul 2004 22:06:26 PDT." <20040706050626.GM18863@pathfinder>
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>  No proof whether I was hitting another entropy bug or just
> workload.  (Reminder to lurkers -- I'm running 1.2 with /dev/random
> major,minor set to 1,9 -- same as /dev/urandom.)

If you temporarily run out of entropy, it should only ever be the
particular user-space process that's reading from /dev/random
that blocks. Everything else should carry on fine in the meantime.

In the unstable tree, AFAIK all interrupt sources are correctly
adding entropy to the kernel's entropy pool -- there are just
fewer bits of entropy generated per second in a VM.

If people are still finding that some heavy users of /dev/random
are blocking unexpectedly (e.g. apache during startup) then we'll
need to think what to do. One grim hack would be to modify the
guest kernel to make it less conservative about its estimate of
entropy generated.  An alternative would be to have Xen handle
entropy generation centrally (from all physical interrupt
sources) and then have a special random driver in each guest.


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