Message-ID: <553977AA.9040802@zytor.com>
Date: Thu, 23 Apr 2015 15:52:26 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0
MIME-Version: 1.0
To: Andy Lutomirski <luto@amacapital.net>
CC: Borislav Petkov <bp@alien8.de>, Denys Vlasenko <vda.linux@googlemail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Brian Gerst <brgerst@gmail.com>, Denys Vlasenko <dvlasenk@redhat.com>,
        Ingo Molnar <mingo@kernel.org>, Steven Rostedt <rostedt@goodmis.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Alexei Starovoitov <ast@plumgrid.com>, Will Drewry <wad@chromium.org>,
        Kees Cook <keescook@chromium.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86/asm/entry/32: Restore %ss before SYSRETL if necessary
References: <1429792491-5978-1-git-send-email-dvlasenk@redhat.com> <CA+55aFwDP1QxvHs9wKE9ZpjAzSHhzc+YQS1Mhwt=oYLrB+Rp1A@mail.gmail.com> <CAMzpN2j3K9B4UDPB8suz15PjoDY2aZBr8bvEZ5r4ag5FLgCVrw@mail.gmail.com> <CA+55aFxre3Jk-CG+mBs6Bp9a1J=riCQaA3dwUTFRph1OsCMSuA@mail.gmail.com> <CALCETrX_RCGH0C4GJ0Zxm1emcasMbZ5s29HCfFy=GrEC9w28+A@mail.gmail.com> <CAK1hOcPp3Xav4iR2mZ4oq4zB5XY+ZNuEds32Rf0Z3fB8A7h1PQ@mail.gmail.com> <20150423211015.GS28327@pd.tnic> <55396617.4020303@zytor.com> <CALCETrVX_O+vu+GJXJKJa7w83DnKn0nrjp2_9xtNdhEJW79XQA@mail.gmail.com> <553972D5.2070104@zytor.com> <CALCETrV2t1ynQ0KpRv71+_1wqUg6d2=k-guqHatrEHJLeJ9d6Q@mail.gmail.com>
In-Reply-To: <CALCETrV2t1ynQ0KpRv71+_1wqUg6d2=k-guqHatrEHJLeJ9d6Q@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 798
Lines: 20

On 04/23/2015 03:38 PM, Andy Lutomirski wrote:
>>
>> Because there are way more sysrets than context switches, and Linux is
>> particularly sensitive to system call latency, by design.
> 

Just to clarify: why would Linux be more sensitive to system call by
design?  It enables much simpler APIs and avoids hacks like sending down
a syscall task list (which was genuinely proposed at one point.)  If
kernel entry/exit is too expensive, then the APIs get more complex
because they *have* to do everything in the smallest number of system calls.

	-hpa


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/