From: Christian Borntraeger <borntraeger@de.ibm.com>
To: Huaisheng Ye <yehs2007@zoho.com>,
linux-nvdimm@lists.01.org, dan.j.williams@intel.com
Cc: axboe@kernel.dk, linux-s390@vger.kernel.org, chengnt@lenovo.com,
linux-fsdevel@vger.kernel.org, heiko.carstens@de.ibm.com,
linux-kernel@vger.kernel.org, willy@infradead.org,
bart.vanassche@wdc.com, viro@zeniv.linux.org.uk,
gregkh@linuxfoundation.org, schwidefsky@de.ibm.com, jack@suse.cz
Subject: Re: [PATCH 3/5] s390, dcssblk: Allow a NULL-kaddr to ->direct_access()
Date: Tue, 24 Jul 2018 10:53:39 +0200 [thread overview]
Message-ID: <192a9dac-921f-e222-3a7d-32d43679cd12@de.ibm.com> (raw)
In-Reply-To: <20180724084510.6104-4-yehs2007@zoho.com>
On 07/24/2018 10:45 AM, Huaisheng Ye wrote:
> From: Huaisheng Ye <yehs1@lenovo.com>
>
> dcssblk_direct_access() needs to check the validity of second rank
> pointer kaddr for NULL assignment. If kaddr equals to NULL, it
> doesn't need to calculate the value.
>
> Signed-off-by: Huaisheng Ye <yehs1@lenovo.com>
> ---
> drivers/s390/block/dcssblk.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
> index 0a312e4..9c13dc5 100644
> --- a/drivers/s390/block/dcssblk.c
> +++ b/drivers/s390/block/dcssblk.c
> @@ -915,7 +915,8 @@ static DEVICE_ATTR(save, S_IWUSR | S_IRUSR, dcssblk_save_show,
> unsigned long dev_sz;
>
> dev_sz = dev_info->end - dev_info->start + 1;
> - *kaddr = (void *) dev_info->start + offset;
> + if (kaddr)
> + *kaddr = (void *) dev_info->start + offset;
So you are trading of a load + add (dev_info->start should be cache hot) against a
compare+branch . Not sure that this is always a win.
> *pfn = __pfn_to_pfn_t(PFN_DOWN(dev_info->start + offset),
> PFN_DEV|PFN_SPECIAL);
>
>
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next prev parent reply other threads:[~2018-07-24 8:53 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-24 8:45 [PATCH 0/5] Do not request a pointer kaddr when not required Huaisheng Ye
2018-07-24 8:45 ` [PATCH 1/5] libnvdimm, pmem: Allow a NULL-kaddr to ->direct_access() Huaisheng Ye
2018-07-24 8:45 ` [PATCH 2/5] tools/testing/nvdimm: " Huaisheng Ye
2018-07-24 8:45 ` [PATCH 3/5] s390, dcssblk: " Huaisheng Ye
2018-07-24 8:53 ` Christian Borntraeger [this message]
2018-07-24 9:46 ` [External] " Huaisheng HS1 Ye
2018-07-24 11:16 ` Christian Borntraeger
2018-07-24 14:28 ` Huaisheng HS1 Ye
2018-07-24 8:45 ` [PATCH 4/5] filesystem-dax: Do not request a pointer kaddr when not required Huaisheng Ye
2018-07-24 8:45 ` [PATCH 5/5] dax/super: " Huaisheng Ye
2018-07-24 14:50 ` [PATCH 0/5] " Ross Zwisler
2018-07-24 15:41 ` [External] " Huaisheng HS1 Ye
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