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[Qemu-devel] Re: Extending virtio_console to support multiple ports
From: |
Amit Shah |
Subject: |
[Qemu-devel] Re: Extending virtio_console to support multiple ports |
Date: |
Mon, 31 Aug 2009 19:21:47 +0530 |
User-agent: |
Mutt/1.5.19 (2009-01-05) |
On (Mon) Aug 31 2009 [08:17:21], Anthony Liguori wrote:
>>>> - A lock has to be introduced to fetch one unused buffer from the list
>>>> and pass it on to the host. And this lock has to be a spinlock, just
>>>> because writes can be called from irq context.
>>>>
>>> I don't see a problem here.
>>>
>>
>> You mean you don't see a problem in using a spinlock vs not using one?
>>
>
> Right. This isn't a fast path.
>
>> Userspace will typically send the entire buffer to be transmitted in one
>> system call. If it's large, the system call will have to be broken into
>> several. This results in multiple guest system calls, each one to be
>> handled with a spinlock held.
>>
>> Compare this with the entire write handled in one system call in the
>> current method.
>>
>
> Does it matter? This isn't a fast path.
The question isn't just about how much work happens inside the spinlock.
It's also a question about introducing spinlocks where they shouldn't
be.
I don't see why such changes have to creep into the kernel.
Can you please explain your rationale for being so rigid about merging
the two drivers?
Amit
- [Qemu-devel] [PATCH] hvc_console: provide (un)locked version for hvc_resize(), (continued)
- [Qemu-devel] [PATCH] hvc_console: provide (un)locked version for hvc_resize(), Hendrik Brueckner, 2009/08/28
- Re: [Qemu-devel] Re: Extending virtio_console to support multiple ports, Jamie Lokier, 2009/08/28
- [Qemu-devel] Re: Extending virtio_console to support multiple ports, Michael Ellerman, 2009/08/28
- [Qemu-devel] Re: Extending virtio_console to support multiple ports, Amit Shah, 2009/08/27
- [Qemu-devel] Re: Extending virtio_console to support multiple ports, Ryan Arnold, 2009/08/28
[Qemu-devel] Re: Extending virtio_console to support multiple ports, Anthony Liguori, 2009/08/28
- [Qemu-devel] Re: Extending virtio_console to support multiple ports, Amit Shah, 2009/08/30
- [Qemu-devel] Re: Extending virtio_console to support multiple ports, Anthony Liguori, 2009/08/30
- [Qemu-devel] Re: Extending virtio_console to support multiple ports, Amit Shah, 2009/08/30
- [Qemu-devel] Re: Extending virtio_console to support multiple ports, Anthony Liguori, 2009/08/31
- [Qemu-devel] Re: Extending virtio_console to support multiple ports,
Amit Shah <=
- [Qemu-devel] Re: Extending virtio_console to support multiple ports, Anthony Liguori, 2009/08/31
- [Qemu-devel] Re: Extending virtio_console to support multiple ports, Amit Shah, 2009/08/31
- [Qemu-devel] Re: Extending virtio_console to support multiple ports, Anthony Liguori, 2009/08/31
- [Qemu-devel] Re: Extending virtio_console to support multiple ports, Amit Shah, 2009/08/31
- [Qemu-devel] Re: Extending virtio_console to support multiple ports, Anthony Liguori, 2009/08/31