netdev - Re: [Xen-devel] [PATCH net-next v1] xen-netback: make copy batch size configurable

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Message-Id: <5A0986F3020000780018E479@prv-mh.provo.novell.com>
Date:   Mon, 13 Nov 2017 03:50:11 -0700
From:   "Jan Beulich" <JBeulich@...e.com>
To:     "Paul Durrant" <Paul.Durrant@...rix.com>
Cc:     "Wei Liu" <wei.liu2@...rix.com>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "'Joao Martins'" <joao.m.martins@...cle.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH net-next v1] xen-netback: make copy
 batch size configurable

>>> On 13.11.17 at 11:33, <Paul.Durrant@...rix.com> wrote:
>> From: Joao Martins [mailto:joao.m.martins@...cle.com]
>> Sent: 10 November 2017 19:35
>> --- a/drivers/net/xen-netback/netback.c
>> +++ b/drivers/net/xen-netback/netback.c
>> @@ -96,6 +96,11 @@ unsigned int xenvif_hash_cache_size =
>> XENVIF_HASH_CACHE_SIZE_DEFAULT;
>>  module_param_named(hash_cache_size, xenvif_hash_cache_size, uint,
>> 0644);

Isn't the "owner-write" permission here ...

>> --- a/drivers/net/xen-netback/rx.c
>> +++ b/drivers/net/xen-netback/rx.c
>> @@ -168,11 +168,14 @@ static void xenvif_rx_copy_add(struct
>> xenvif_queue *queue,
>>  			       struct xen_netif_rx_request *req,
>>  			       unsigned int offset, void *data, size_t len)
>>  {
>> +	unsigned int batch_size;
>>  	struct gnttab_copy *op;
>>  	struct page *page;
>>  	struct xen_page_foreign *foreign;
>> 
>> -	if (queue->rx_copy.num == COPY_BATCH_SIZE)
>> +	batch_size = min(xenvif_copy_batch_size, queue->rx_copy.size);
> 
> Surely queue->rx_copy.size and xenvif_copy_batch_size are always identical? 
> Why do you need this statement (and hence stack variable)?

... the answer to your question?

Jan