netdev - Re: CONFIG_XPS depends on L1_CACHE_BYTES being greater than sizeof(struct xps

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Message-ID: <CALx6S351U9L43Qh88DkJSM4tmhR-7SDoC6bCEhNqxnuu8LqTNA@mail.gmail.com>
Date:	Thu, 22 Oct 2015 14:37:31 -0700
From:	Tom Herbert <tom@...bertland.com>
To:	Helge Deller <deller@....de>
Cc:	Tom Herbert <therbert@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	linux-parisc List <linux-parisc@...r.kernel.org>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	John David Anglin <dave.anglin@...l.net>
Subject: Re: CONFIG_XPS depends on L1_CACHE_BYTES being greater than
 sizeof(struct xps_map)

On Thu, Oct 22, 2015 at 1:00 PM, Helge Deller <deller@....de> wrote:
> Hi Tom & David,
>
> I've queued-up a patch for the parisc architecture which reduces L1_CACHE_BYTES from 32 to 16:
>   https://patchwork.kernel.org/patch/7399291/
>
> But this change will break the kernel build like this:
>
> In file included from net/core/dev.c:92:0:
> net/core/dev.c: In function ‘expand_xps_map’:
> include/linux/netdevice.h:721:27: warning: overflow in implicit constant conversion [-Woverflow]
>    #define XPS_MIN_MAP_ALLOC ((L1_CACHE_BYTES - sizeof(struct xps_map)) \
> net/core/dev.c:1972:18: note: in expansion of macro ‘XPS_MIN_MAP_ALLOC’
>    int alloc_len = XPS_MIN_MAP_ALLOC;
>
> Do you see an easy way to fix this ?
>
How about

 #define XPS_MIN_MAP_ALLOC ((L1_CACHE_BYTES - ((sizeof(struct xps_map)
% L1_CACHE_BYTES)) \

Tom

> Thanks,
> Helge
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