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Re: [Qemu-devel] [RFC PATCH RDMA support v6: 4/7] Introduce two new capa

From: Michael R. Hines
Subject: Re: [Qemu-devel] [RFC PATCH RDMA support v6: 4/7] Introduce two new capabilities
Date: Wed, 10 Apr 2013 09:10:46 -0400
User-agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130106 Thunderbird/17.0.2

On 04/10/2013 08:40 AM, Paolo Bonzini wrote:
Il 10/04/2013 14:34, Michael R. Hines ha scritto:
On 04/10/2013 03:50 AM, Paolo Bonzini wrote:
Il 10/04/2013 06:29, address@hidden ha scritto:
From: "Michael R. Hines" <address@hidden>

RDMA performs very slowly with zero-page checking.
Without the ability to disable it, RDMA throughput and
latency promises and high performance links cannot be
fully realized.

On the other hand, dynamic page registration support is also
included in the RDMA protocol. This second capability also
cannot be fully realized without the ability to enable zero
page scanning.

So, we have two new capabilities which work together:

1. migrate_set_capability check_for_zero on|off (default on)
2. migrate_set_capability chunk_register_destination on|off (default

Signed-off-by: Michael R. Hines <address@hidden>
Michael, please listen to _all_ review comments.

1) I asked you to place check_for_zero in a separate patch.

2) Again, patch 3 cannot compile without this one.  The code should
compile after each patch, with and without --enable-rdma.
My apologies - I misunderstood the request. I am indeed addressing every

When you said separate, I thought you meant a different patch series

This is my first time, so the meaning of "separate" was not clear =)

And yes, patch 3 does in fact compile both with and without --enable-rdma.
How does this:

+const QEMURamControlOps qemu_rdma_write_control = {
+    .before_ram_iterate = qemu_ram_registration_start,
+    .after_ram_iterate = qemu_rdma_registration_stop,
+    .register_ram_iterate = qemu_rdma_registration_handle,
+    .save_page = qemu_rdma_save_page,

compile (and link) successfully without a definition of
qemu_ram_registration_start, which is in patch 5?  (Honest question).

Similarly, patch 5 cannot link without qemu_ram_foreach_block.

Anyway, patch 1 does not compile with --enable-rdma. :)

Yes, all 7 patches do compile in both cases - that code is conditionalized with CONFIG_RDMA.

What exactly is the problem there?

I toggled the enable/disable flags several times and recompiled just to be sure.

Also about qemu_ram_foreach_block: Why does this depend on patch 5, exactly?

qemu_ram_foreach_block is not conditionalized by anything.

You flip-flopped on me =)
You said conditionalize it, then make a separate patch, then delete it
altogether =)
Make qemu_set_nonblock conditional, dropping the assert.

Do not touch the implementation of qemu_set_nonblock.  (Yes, this was a



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