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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
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

  reply index

Thread overview: 27+ 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 ` [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 ` [patch 03/12] USB: serial: keyspan_pda: Consolidate room query Thomas Gleixner
2020-10-14 16:14   ` Alan Stern
2020-10-14 16:17     ` Thomas Gleixner
2020-10-14 16:27     ` Sebastian Andrzej Siewior
2020-10-14 16:34       ` Alan Stern [this message]
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 ` [patch 05/12] usb: xhci: Remove in_interrupt() checks Thomas Gleixner
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 ` [patch 07/12] usbip: Remove in_interrupt() check Thomas Gleixner
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 15:24   ` Krzysztof Kozlowski
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 ` [patch 10/12] usb: gadget: udc: Remove in_interrupt()/in_irq() from comments Thomas Gleixner
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 16:27   ` Alan Stern
2020-10-14 16:41     ` Sebastian Andrzej Siewior
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
2020-10-23  8:01 ` [patch 00/12] UBS: Cleanup in_interupt/in_irq/in_atomic() usage Pavel Machek

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