From: Alan Stern <stern@rowland.harvard.edu>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Johan Hovold <johan@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-usb@vger.kernel.org,
Thomas Winischhofer <thomas@winischhofer.net>,
"Ahmed S. Darwish" <a.darwish@linutronix.de>,
Mathias Nyman <mathias.nyman@intel.com>,
Valentina Manea <valentina.manea.m@gmail.com>,
Shuah Khan <shuah@kernel.org>,
linux-omap@vger.kernel.org, Kukjin Kim <kgene@kernel.org>,
Krzysztof Kozlowski <krzk@kernel.org>,
linux-arm-kernel@lists.infradead.org,
linux-samsung-soc@vger.kernel.org,
Felipe Balbi <balbi@kernel.org>,
Duncan Sands <duncan.sands@free.fr>
Subject: Re: [patch 03/12] USB: serial: keyspan_pda: Consolidate room query
Date: Wed, 14 Oct 2020 12:34:25 -0400 [thread overview]
Message-ID: <20201014163425.GF712494@rowland.harvard.edu> (raw)
In-Reply-To: <20201014162714.ctv5earlhwsp4iqs@linutronix.de>
On Wed, Oct 14, 2020 at 06:27:14PM +0200, Sebastian Andrzej Siewior wrote:
> On 2020-10-14 12:14:33 [-0400], Alan Stern wrote:
> > Instead, consider using the new usb_control_msg_recv() API. But it
> > might be better to allocate the buffer once and for all.
>
> This will still allocate and free buffer on each invocation. What about
Yes. That's why I suggesting doing a single buffer allocation at the
start and using it for each I/O transfer. (But I'm not familiar with
this code, and I don't know if there might be multiple transfers going
on concurrently.)
> moving the query_buf to the begin of the struct / align it?
No, thank won't work either. The key to the issue is that while some
memory is mapped for DMA, the CPU must not touch it or anything else in
the same cache line. If a field is a member of a data structure, the
CPU might very well access a neighboring member while this one is
mapped, thereby messing up the cache line.
Alan Stern
WARNING: multiple messages have this Message-ID (diff)
From: Alan Stern <stern@rowland.harvard.edu>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Felipe Balbi <balbi@kernel.org>,
Thomas Winischhofer <thomas@winischhofer.net>,
Mathias Nyman <mathias.nyman@intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-usb@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
Krzysztof Kozlowski <krzk@kernel.org>,
Johan Hovold <johan@kernel.org>,
linux-samsung-soc@vger.kernel.org, Kukjin Kim <kgene@kernel.org>,
Valentina Manea <valentina.manea.m@gmail.com>,
Duncan Sands <duncan.sands@free.fr>,
"Ahmed S. Darwish" <a.darwish@linutronix.de>,
Thomas Gleixner <tglx@linutronix.de>,
linux-omap@vger.kernel.org, Shuah Khan <shuah@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [patch 03/12] USB: serial: keyspan_pda: Consolidate room query
Date: Wed, 14 Oct 2020 12:34:25 -0400 [thread overview]
Message-ID: <20201014163425.GF712494@rowland.harvard.edu> (raw)
In-Reply-To: <20201014162714.ctv5earlhwsp4iqs@linutronix.de>
On Wed, Oct 14, 2020 at 06:27:14PM +0200, Sebastian Andrzej Siewior wrote:
> On 2020-10-14 12:14:33 [-0400], Alan Stern wrote:
> > Instead, consider using the new usb_control_msg_recv() API. But it
> > might be better to allocate the buffer once and for all.
>
> This will still allocate and free buffer on each invocation. What about
Yes. That's why I suggesting doing a single buffer allocation at the
start and using it for each I/O transfer. (But I'm not familiar with
this code, and I don't know if there might be multiple transfers going
on concurrently.)
> moving the query_buf to the begin of the struct / align it?
No, thank won't work either. The key to the issue is that while some
memory is mapped for DMA, the CPU must not touch it or anything else in
the same cache line. If a field is a member of a data structure, the
CPU might very well access a neighboring member while this one is
mapped, thereby messing up the cache line.
Alan Stern
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linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-10-14 16:34 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-14 14:52 [patch 00/12] UBS: Cleanup in_interupt/in_irq/in_atomic() usage Thomas Gleixner
2020-10-14 14:52 ` Thomas Gleixner
2020-10-14 14:52 ` [patch 01/12] USB: sisusbvga: Make console support depend on BROKEN Thomas Gleixner
2020-10-14 14:52 ` [patch 02/12] USB: serial: keyspan_pda: Replace in_interrupt() usage Thomas Gleixner
2020-10-14 14:52 ` Thomas Gleixner
2020-10-14 14:52 ` [patch 03/12] USB: serial: keyspan_pda: Consolidate room query Thomas Gleixner
2020-10-14 14:52 ` Thomas Gleixner
2020-10-14 16:14 ` Alan Stern
2020-10-14 16:14 ` Alan Stern
2020-10-14 16:17 ` Thomas Gleixner
2020-10-14 16:17 ` Thomas Gleixner
2020-10-14 16:27 ` Sebastian Andrzej Siewior
2020-10-14 16:27 ` Sebastian Andrzej Siewior
2020-10-14 16:34 ` Alan Stern [this message]
2020-10-14 16:34 ` Alan Stern
2020-10-14 16:44 ` Sebastian Andrzej Siewior
2020-10-14 16:44 ` Sebastian Andrzej Siewior
2020-10-14 14:52 ` [patch 04/12] USB: serial: digi_acceleport: Remove in_interrupt() usage Thomas Gleixner
2020-10-14 14:52 ` Thomas Gleixner
2020-10-14 14:52 ` [patch 05/12] usb: xhci: Remove in_interrupt() checks Thomas Gleixner
2020-10-14 14:52 ` Thomas Gleixner
2020-10-23 13:38 ` Mathias Nyman
2020-10-23 13:38 ` Mathias Nyman
2020-10-14 14:52 ` [patch 06/12] usb: host: isp1362: Replace in_interrupt() usage Thomas Gleixner
2020-10-14 14:52 ` Thomas Gleixner
2020-10-14 18:49 ` kernel test robot
2020-10-14 18:49 ` kernel test robot
2020-10-14 14:52 ` [patch 07/12] usbip: Remove in_interrupt() check Thomas Gleixner
2020-10-14 14:52 ` Thomas Gleixner
2020-10-14 15:45 ` Shuah Khan
2020-10-14 15:45 ` Shuah Khan
2020-10-14 14:52 ` [patch 08/12] usb: hosts: Remove in_interrupt() from comments Thomas Gleixner
2020-10-14 14:52 ` Thomas Gleixner
2020-10-14 15:24 ` Krzysztof Kozlowski
2020-10-14 15:24 ` Krzysztof Kozlowski
2020-10-14 16:20 ` Alan Stern
2020-10-14 16:20 ` Alan Stern
2020-10-14 14:52 ` [patch 09/12] usb: gadget: pxa27x_udc: Replace in_interrupt() usage in comments Thomas Gleixner
2020-10-14 14:52 ` Thomas Gleixner
2020-10-14 14:52 ` [patch 10/12] usb: gadget: udc: Remove in_interrupt()/in_irq() from comments Thomas Gleixner
2020-10-14 14:52 ` Thomas Gleixner
2020-10-14 16:22 ` Alan Stern
2020-10-14 16:22 ` Alan Stern
2020-10-14 14:52 ` [patch 11/12] usb: core: Replace in_interrupt() in comments Thomas Gleixner
2020-10-14 14:52 ` Thomas Gleixner
2020-10-14 16:27 ` Alan Stern
2020-10-14 16:27 ` Alan Stern
2020-10-14 16:41 ` Sebastian Andrzej Siewior
2020-10-14 16:41 ` Sebastian Andrzej Siewior
2020-10-14 18:13 ` Alan Stern
2020-10-14 18:13 ` Alan Stern
2020-10-14 14:52 ` [patch 12/12] usb: atm: Replace in_interrupt() usage in comment Thomas Gleixner
2020-10-14 14:52 ` Thomas Gleixner
2020-10-23 8:01 ` [patch 00/12] UBS: Cleanup in_interupt/in_irq/in_atomic() usage Pavel Machek
2020-10-23 8:01 ` Pavel Machek
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