From: Thomas Gleixner <tglx@linutronix.de>
To: "Luck, Tony" <tony.luck@intel.com>
Cc: Borislav Petkov <bp@alien8.de>, Dave Jiang <dave.jiang@intel.com>,
dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org,
vkoul@kernel.org, dan.j.williams@intel.com, jing.lin@intel.com,
ashok.raj@intel.com, sanjay.k.kumar@intel.com,
megha.dey@intel.com, jacob.jun.pan@intel.com, yi.l.liu@intel.com,
axboe@kernel.dk, akpm@linux-foundation.org, mingo@redhat.com,
fenghua.yu@intel.com, hpa@zytor.com
Subject: Re: [PATCH RFC 01/14] x86/asm: add iosubmit_cmds512() based on movdir64b CPU instruction
Date: Thu, 21 Nov 2019 01:22:41 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.21.1911210120410.29534@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20191120231923.GA32680@agluck-desk2.amr.corp.intel.com>
On Wed, 20 Nov 2019, Luck, Tony wrote:
> On Wed, Nov 20, 2019 at 10:53:39PM +0100, Borislav Petkov wrote:
> > On Wed, Nov 20, 2019 at 02:23:49PM -0700, Dave Jiang wrote:
> > > +static inline void iosubmit_cmds512(void __iomem *dst, const void *src,
> > > + size_t count)
> >
> > An iosubmit function which returns void and doesn't tell its callers
> > whether it succeeded or not? That looks non-optimal to say the least.
>
> That's the underlying functionality of the MOVDIR64B instruction. A
> posted write so no way to know if it succeeded. When using dedicated
> queues the caller must keep count of how many operations are in flight
> and not send more than the depth of the queue.
>
> > Why isn't there a fallback function which to call when the CPU doesn't
> > support movdir64b?
>
> This particular driver has no option for fallback. Descriptors can
> only be submitted with MOVDIR64B (to dedicated queues ... in later
> patch series support for shared queues will be added, but those require
> ENQCMD or ENQCMDS to submit).
>
> The driver bails out at the beginning of the probe routine if the
> necessary instructions are not supported:
>
> + /*
> + * If the CPU does not support write512, there's no point in
> + * enumerating the device. We can not utilize it.
> + */
> + if (!cpu_has_write512())
> + return -ENXIO;
>
> Though we should always get past that as this PCI device ID shouldn't
> every appear on a system that doesn't have the support. Device is on
> the die, not a plug-in card.
Then the condition in the iosubmit function is just prone to silently paper
over any bug in a driver:
> + if (!cpu_has_write512())
> + return;
This should at least issue a WARN_ON_ONCE()
Thanks,
tglx
next prev parent reply other threads:[~2019-11-21 0:22 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-20 21:23 [PATCH RFC 00/14] idxd driver for Intel Data Streaming Accelerator Dave Jiang
2019-11-20 21:23 ` [PATCH RFC 01/14] x86/asm: add iosubmit_cmds512() based on movdir64b CPU instruction Dave Jiang
2019-11-20 21:50 ` Dave Hansen
2019-11-20 23:46 ` Dave Jiang
2019-11-20 21:53 ` Borislav Petkov
2019-11-20 23:19 ` Luck, Tony
2019-11-20 23:26 ` Borislav Petkov
2019-11-21 0:15 ` Luck, Tony
2019-11-21 0:27 ` Dan Williams
2019-11-21 0:53 ` Thomas Gleixner
2019-11-21 1:32 ` Dan Williams
2019-11-21 10:37 ` Borislav Petkov
2019-11-21 0:21 ` Dan Williams
2019-11-21 0:22 ` Thomas Gleixner [this message]
2019-11-21 0:27 ` Dave Jiang
2019-11-21 0:10 ` Dave Jiang
2019-11-21 10:59 ` Borislav Petkov
2019-11-21 16:52 ` Dave Jiang
2019-11-22 8:59 ` Borislav Petkov
2019-11-22 17:20 ` Dan Williams
2019-11-22 18:44 ` Borislav Petkov
2019-11-22 18:50 ` Dan Williams
2019-11-20 21:23 ` [PATCH RFC 02/14] dmaengine: break out channel registration Dave Jiang
2019-11-20 21:24 ` [PATCH RFC 03/14] dmaengine: add new dma device registration Dave Jiang
2019-11-20 21:24 ` [PATCH RFC 04/14] mm: create common code from request allocation based from blk-mq code Dave Jiang
2019-11-20 21:24 ` [PATCH RFC 05/14] dmaengine: add dma_request support functions Dave Jiang
2019-11-20 21:24 ` [PATCH RFC 06/14] dmaengine: add dma request submit and completion path support Dave Jiang
2019-11-20 21:24 ` [PATCH RFC 07/14] dmaengine: update dmatest to support dma request Dave Jiang
2019-11-20 21:24 ` [PATCH RFC 08/14] dmaengine: idxd: Init and probe for Intel data accelerators Dave Jiang
2019-11-20 21:24 ` [PATCH RFC 09/14] dmaengine: idxd: add configuration component of driver Dave Jiang
2019-11-20 21:24 ` [PATCH RFC 10/14] dmaengine: idxd: add descriptor manipulation routines Dave Jiang
2019-11-20 21:24 ` [PATCH RFC 11/14] dmaengine: idxd: connect idxd to dmaengine subsystem Dave Jiang
2019-11-20 21:24 ` [PATCH RFC 12/14] dmaengine: request submit optimization Dave Jiang
2019-11-20 21:25 ` [PATCH RFC 13/14] dmaengine: idxd: add char driver to expose submission portal to userland Dave Jiang
2019-11-20 21:25 ` [PATCH RFC 14/14] dmaengine: idxd: add sysfs ABI for idxd driver Dave Jiang
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