Message-ID: <54E60DB5.5070509@oracle.com>
Date: Thu, 19 Feb 2015 09:22:13 -0700
From: David Ahern <david.ahern@oracle.com>
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0) Gecko/20100101 Thunderbird/31.4.0
MIME-Version: 1.0
To: Adrian Hunter <adrian.hunter@intel.com>, David Ahern <dsahern@gmail.com>,
        acme@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] perf: Fix probing for PERF_FLAG_FD_CLOEXEC flag
References: <1424304072-91955-1-git-send-email-david.ahern@oracle.com> <54E58B64.9010902@intel.com> <54E5F963.50200@gmail.com> <54E60CA0.6020001@intel.com>
In-Reply-To: <54E60CA0.6020001@intel.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1174
Lines: 22

On 2/19/15 9:17 AM, Adrian Hunter wrote:
> Yes, I am sorry it is a pain. I don't know why I didn't add a comment
> to the code :-(. Using -1 for the pid is a workaround to avoid gratuitous
> jump label changes. If pid=0 is used and then a system-wide trace is done
> with Intel PT, there will be a jump label change shortly after the tracing
> starts. That means the running code gets changed, but Intel PT decoding
> has to walk the code to reconstruct the trace - so errors result. There
> will always be occasional jump label changes, but this avoids one that
> would otherwise always happen.

I don't understand the response. Why can't pid == getpid() (ie., pid > 
0) be used for this test? pid = -1 and pid = 0 are not needed. With pid 
 > 0 cpu value does not matter so cpu = -1 can be used. Again this is 
just to determine if the kernel supports PERF_FLAG_FD_CLOEXEC. Existence 
of PT should not be involved here.

David
--
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/