From: Al Viro <viro@zeniv.linux.org.uk>
To: afzal mohammed <afzal.mohd.ma@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
Russell King - ARM Linux admin <linux@armlinux.org.uk>,
Linus Walleij <linus.walleij@linaro.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Nicolas Pitre <nico@fluxnic.net>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>
Subject: Re: [RFC 1/3] lib: copy_{from,to}_user using gup & kmap_atomic()
Date: Sat, 13 Jun 2020 16:41:18 +0100 [thread overview]
Message-ID: <20200613154118.GH23230@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20200613153102.GG23230@ZenIV.linux.org.uk>
On Sat, Jun 13, 2020 at 04:31:02PM +0100, Al Viro wrote:
> On Sat, Jun 13, 2020 at 07:12:36PM +0530, afzal mohammed wrote:
> > Hi,
> >
> > On Sat, Jun 13, 2020 at 01:56:15PM +0100, Al Viro wrote:
> >
> > > Incidentally, what about get_user()/put_user()? _That_ is where it's
> > > going to really hurt...
> >
> > All other uaccess routines are also planned to be added, posting only
> > copy_{from,to}_user() was to get early feedback (mentioned in the
> > cover letter)
>
> Sure, but what I mean is that I'd expect the performance loss to be
> dominated by that, not by copy_from_user/copy_to_user on large amounts
> of data. Especially on the loads like kernel builds - a lot of stat()
> and getdents() calls there.
To clarify: stat() means small copy_to_user(), getdents() - a mix of
put_user() and small copy_to_user(). I would be very surprised if it
does not hurt a lot.
next prev parent reply other threads:[~2020-06-13 15:41 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-12 10:17 [RFC 0/3] ARM: copy_{from,to}_user() for vmsplit 4g/4g afzal mohammed
2020-06-12 10:17 ` [RFC 1/3] lib: copy_{from,to}_user using gup & kmap_atomic() afzal mohammed
2020-06-12 12:02 ` Arnd Bergmann
2020-06-12 13:55 ` afzal mohammed
2020-06-12 20:07 ` Arnd Bergmann
2020-06-13 12:04 ` afzal mohammed
2020-06-13 12:51 ` Al Viro
2020-06-13 12:56 ` Al Viro
2020-06-13 13:42 ` afzal mohammed
2020-06-13 15:31 ` Al Viro
2020-06-13 15:41 ` Al Viro [this message]
2020-06-13 16:00 ` Al Viro
2020-06-13 18:55 ` Arnd Bergmann
2020-06-13 13:15 ` Russell King - ARM Linux admin
2020-06-14 13:06 ` afzal mohammed
2020-06-13 20:45 ` Arnd Bergmann
2020-06-13 22:16 ` Matthew Wilcox
2020-06-14 13:21 ` afzal mohammed
2020-06-14 14:55 ` afzal mohammed
2020-06-13 11:08 ` Andy Shevchenko
2020-06-13 13:29 ` afzal mohammed
2020-06-12 10:18 ` [RFC 2/3] ARM: uaccess: let UACCESS_GUP_KMAP_MEMCPY enabling afzal mohammed
2020-06-12 10:18 ` [RFC 3/3] ARM: provide CONFIG_VMSPLIT_4G_DEV for development afzal mohammed
2020-06-12 15:19 ` [RFC 0/3] ARM: copy_{from,to}_user() for vmsplit 4g/4g Nicolas Pitre
2020-06-12 16:01 ` afzal mohammed
2020-06-12 16:03 ` afzal mohammed
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