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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Alan Stern <stern@rowland.harvard.edu>
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 18:44:43 +0200	[thread overview]
Message-ID: <20201014164443.husmibyqb4ukw5xg@linutronix.de> (raw)
In-Reply-To: <20201014163425.GF712494@rowland.harvard.edu>

On 2020-10-14 12:34:25 [-0400], Alan Stern wrote:
> 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.)

There are no concurrent transfer. There is a bit used as a lock. The
first one does the transfer, the other wait.

> > 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.

that is unfortunately true. Let me do the single buffer.

> Alan Stern

Sebastian

  reply	other threads:[~2020-10-14 16:44 UTC|newest]

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
2020-10-14 16:44         ` Sebastian Andrzej Siewior [this message]
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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