netdev - Re: [PATCH v2] ocfs2/dlm: Move BITS_TO_BYTES() to bitops.h for wider use

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Date:   Mon, 9 Dec 2019 18:43:38 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Mark Fasheh <mark@...heh.com>, Joel Becker <jlbec@...lplan.org>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        ocfs2-devel@....oracle.com, Ariel Elior <aelior@...vell.com>,
        Sudarsana Kalluru <skalluru@...vell.com>,
        GR-everest-linux-l2@...vell.com,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Colin Ian King <colin.king@...onical.com>
Subject: Re: [PATCH v2] ocfs2/dlm: Move BITS_TO_BYTES() to bitops.h for wider
 use

On Tue, Aug 27, 2019 at 07:37:17PM +0300, Andy Shevchenko wrote:
> There are users already and will be more of BITS_TO_BYTES() macro.
> Move it to bitops.h for wider use.
> 
> In the case of ocfs2 the replacement is identical.
> 
> As for bnx2x, there are two places where floor version is used.
> In the first case to calculate the amount of structures that can fit
> one memory page. In this case obviously the ceiling variant is correct and
> original code might have a potential bug, if amount of bits % 8 is not 0.
> In the second case the macro is used to calculate bytes transmitted in one
> microsecond. This will work for all speeds which is multiply of 1Gbps without
> any change, for the rest new code will give ceiling value, for instance 100Mbps
> will give 13 bytes, while old code gives 12 bytes and the arithmetically
> correct one is 12.5 bytes. Further the value is used to setup timer threshold
> which in any case has its own margins due to certain resolution. I don't see
> here an issue with slightly shifting thresholds for low speed connections, the
> card is supposed to utilize highest available rate, which is usually 10Gbps.

Anybody to comment on bnx2 change?
Can we survive with this applied?

> 
> Reviewed-by: Joseph Qi <joseph.qi@...ux.alibaba.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
> - described bnx2x cases in the commit message
> - appended Rb (for ocfs2)
> 
>  drivers/net/ethernet/broadcom/bnx2x/bnx2x_init.h | 1 -
>  fs/ocfs2/dlm/dlmcommon.h                         | 4 ----
>  include/linux/bitops.h                           | 1 +
>  3 files changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/broadcom/bnx2x/bnx2x_init.h b/drivers/net/ethernet/broadcom/bnx2x/bnx2x_init.h
> index 066765fbef06..0a59a09ef82f 100644
> --- a/drivers/net/ethernet/broadcom/bnx2x/bnx2x_init.h
> +++ b/drivers/net/ethernet/broadcom/bnx2x/bnx2x_init.h
> @@ -296,7 +296,6 @@ static inline void bnx2x_dcb_config_qm(struct bnx2x *bp, enum cos_mode mode,
>   *    possible, the driver should only write the valid vnics into the internal
>   *    ram according to the appropriate port mode.
>   */
> -#define BITS_TO_BYTES(x) ((x)/8)
>  
>  /* CMNG constants, as derived from system spec calculations */
>  
> diff --git a/fs/ocfs2/dlm/dlmcommon.h b/fs/ocfs2/dlm/dlmcommon.h
> index aaf24548b02a..0463dce65bb2 100644
> --- a/fs/ocfs2/dlm/dlmcommon.h
> +++ b/fs/ocfs2/dlm/dlmcommon.h
> @@ -688,10 +688,6 @@ struct dlm_begin_reco
>  	__be32 pad2;
>  };
>  
> -
> -#define BITS_PER_BYTE 8
> -#define BITS_TO_BYTES(bits) (((bits)+BITS_PER_BYTE-1)/BITS_PER_BYTE)
> -
>  struct dlm_query_join_request
>  {
>  	u8 node_idx;
> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> index cf074bce3eb3..79d80f5ddf7b 100644
> --- a/include/linux/bitops.h
> +++ b/include/linux/bitops.h
> @@ -5,6 +5,7 @@
>  #include <linux/bits.h>
>  
>  #define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE)
> +#define BITS_TO_BYTES(nr)	DIV_ROUND_UP(nr, BITS_PER_BYTE)
>  #define BITS_TO_LONGS(nr)	DIV_ROUND_UP(nr, BITS_PER_TYPE(long))
>  
>  extern unsigned int __sw_hweight8(unsigned int w);
> -- 
> 2.23.0.rc1
> 

-- 
With Best Regards,
Andy Shevchenko