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Date: Thu, 09 Aug 2012 18:12:39 +0900
From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
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Subject: Re: [Qemu-devel] [RFC PATCH 1/6] virtio/console: Add splice_write
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To: Amit Shah <amit.shah@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>, qemu-devel@nongnu.org, Frederic Weisbecker <fweisbec@gmail.com>, Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>, yrl.pp-manager.tt@hitachi.com, linux-kernel@vger.kernel.org, Borislav Petkov <bp@amd64.org>, virtualization@lists.linux-foundation.org, Herbert Xu <herbert@gondor.hengli.com.au>, "Franch Ch. Eigler" <fche@redhat.com>, Ingo Molnar <mingo@redhat.com>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Steven Rostedt <rostedt@goodmis.org>, Anthony Liguori <anthony@codemonkey.ws>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>

(2012/08/09 18:00), Amit Shah wrote:
> On (Tue) 24 Jul 2012 [11:37:07], Yoshihiro YUNOMAE wrote:
>> From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
>>
>> Enable to use splice_write from pipe to virtio-console port.
>> This steals pages from pipe and directly send it to host.
>>
>> Note that this may accelerate only the guest to host path.
>>
>> Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
>> Cc: Amit Shah <amit.shah@redhat.com>
>> Cc: Arnd Bergmann <arnd@arndb.de>
>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> ---
> 
>> +/* Faster zero-copy write by splicing */
>> +static ssize_t port_fops_splice_write(struct pipe_inode_info *pipe,
>> +				      struct file *filp, loff_t *ppos,
>> +				      size_t len, unsigned int flags)
>> +{
>> +	struct port *port = filp->private_data;
>> +	struct sg_list sgl;
>> +	ssize_t ret;
>> +	struct splice_desc sd = {
>> +		.total_len = len,
>> +		.flags = flags,
>> +		.pos = *ppos,
>> +		.u.data = &sgl,
>> +	};
>> +
>> +	sgl.n = 0;
>> +	sgl.len = 0;
>> +	sgl.sg = kmalloc(sizeof(struct scatterlist) * MAX_SPLICE_PAGES,
>> +			 GFP_ATOMIC);
> 
> Do you expect this function to be called from interrupt context?

No, not at all. Oops, that should be GFP_KERNEL...

Thank you for pointing it out.

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com