Re: [PATCH v9 1/2] Documentation: kdump: remind user of nr_cpus
On 08/19/2016 11:57 PM, Jonathan Corbet wrote: On Fri, 19 Aug 2016 08:33:21 +0800 "Zhou, Wenjian/周文剑" <zhouwj-f...@cn.fujitsu.com> wrote: I was also confused by maxcpus and nr_cpus before writing this patch. I think it is a good choice to describe it in kernel-parameters.txt. Then, only two things need to be done I think. One is move the above description to maxcpus= in kernel-parameters.txt. And the other is replace maxcpus with maxcpus/nr_cpus in kdump.txt. How do you think? That is not quite what I had in mind, sorry. What I would really like to see in kernel-parameters.txt is an explanation of how those two parameters differ - what do they do differently and how should a user choose one over the other? What we have now offers no guidance in that matter. I thought about it. I think user may not need this. What user really want to know is how to choose. And it is also not a hard work. If nr_cpus is not supported by the ARCH, use maxcpus. Otherwise, nr_cpus. The reason why maxcpus still exists is nr_cpus can't be supported by some ARCHes. I think it may be why the author didn't write too much description of it. I suspect that may be a bit more than you had signed up to do. As an intermediate step, how about this: rather than tacking on those lines in kdump.txt, rewrite that paragraph to simply say what the reader should use. If nr_cpus is good for everybody, just say that, but your previous patch suggests that the situation isn't quite that simple? Actually, if nr_cpus always usable, there won't be these discussions. -- Thanks Zhou -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH v9 1/2] Documentation: kdump: remind user of nr_cpus
Hi Jonathan, Thanks for your reply. On 08/19/2016 01:18 AM, Jonathan Corbet wrote: On Thu, 18 Aug 2016 11:11:46 +0800 Zhou Wenjian <zhouwj-f...@cn.fujitsu.com> wrote: Thank you for working to improve the documentation! * We generally don' have to bring up a SMP kernel just to capture the dump. Hence generally it is useful either to build a UP dump-capture kernel or specify maxcpus=1 option while loading dump-capture kernel. + Note, though maxcpus always works, you should replace it by nr_cpus to + save memory if supported by the current ARCH, such as x86. So, IMHO, this seems like the wrong place for this. I've just spent a bit of time staring at kernel-parameters.txt, and there is no way for a clueless user like me to know what the difference is between maxcpus= and nr_cpus= would be. A far better patch would be to update the documentation there to make that clear. Any chance you would be willing to do that? Then, rather than tacking an "ignore what you just read" note into kdump.txt, it could maybe be rewritten to simply say what users should do? I was also confused by maxcpus and nr_cpus before writing this patch. I think it is a good choice to describe it in kernel-parameters.txt. Then, only two things need to be done I think. One is move the above description to maxcpus= in kernel-parameters.txt. And the other is replace maxcpus with maxcpus/nr_cpus in kdump.txt. How do you think? -- Thanks Zhou -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH v8 1/2] Documentation: kdump: remind user of nr_cpus
On 08/18/2016 02:47 PM, Dave Young wrote: On 08/17/16 at 07:36pm, Joe Perches wrote: On Thu, 2016-08-18 at 10:31 +0800, Zhou Wenjian wrote: nr_cpus can help to save memory. So we should remind user of it. trivia: diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt [] @@ -390,9 +390,11 @@ Notes on loading the dump-capture kernel: * Boot parameter "1" boots the dump-capture kernel into single-user mode without networking. If you want networking, use "3". -* We generally don' have to bring up a SMP kernel just to capture the +* We generally don' have to bring up an SMP kernel just to capture the don't or do not Use do not is better, also need replace 'We' with 'You' to be consistent with other part. I think it's better to fix it in another patch, for it doesn't have much relevance to the patch set. I'll post it alone later. -- Thanks Zhou -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH v9 1/2] Documentation: kdump: remind user of nr_cpus
nr_cpus can help to save memory. So we should remind user of it. Signed-off-by: Zhou Wenjian <zhouwj-f...@cn.fujitsu.com> Acked-by: Baoquan He <b...@redhat.com> Acked-by: Xunlei Pang <xp...@redhat.com> --- Documentation/kdump/kdump.txt | 2 ++ 1 file changed, 2 insertions(+) diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt index 88ff63d..d900080 100644 --- a/Documentation/kdump/kdump.txt +++ b/Documentation/kdump/kdump.txt @@ -393,6 +393,8 @@ Notes on loading the dump-capture kernel: * We generally don' have to bring up a SMP kernel just to capture the dump. Hence generally it is useful either to build a UP dump-capture kernel or specify maxcpus=1 option while loading dump-capture kernel. + Note, though maxcpus always works, you should replace it by nr_cpus to + save memory if supported by the current ARCH, such as x86. * For s390x there are two kdump modes: If a ELF header is specified with the elfcorehdr= kernel parameter, it is used by the kdump kernel as it -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH v9 0/2] update the doc of kdump
v8->v9: rearrange the patch. it won't fix typo which original exists. those should be fixed in other patch, which I'll post later. v7->v8: fix "a SMP kernel" to "an SMP kernel" and replace "\" with "/" v6->v7: fix typo v5->v6: replace "we" with "you" v4->v5: move change log to cover letter v3->v4: update the description of bring up SMP dump-capture kernel v2->v3: add description of nr_cpus. v1->v2: change nr_cpus to maxcpus Zhou Wenjian (2): Documentation: kdump: remind user of nr_cpus Documentation: kdump: add description of enable multi-cpus support Documentation/kdump/kdump.txt | 9 + 1 file changed, 9 insertions(+) -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH v9 2/2] Documentation: kdump: add description of enable multi-cpus support
multi-cpu support is useful to improve the performance of kdump in some cases. So add the description of enable multi-cpu support in dump-capture kernel. Signed-off-by: Zhou Wenjian <zhouwj-f...@cn.fujitsu.com> Acked-by: Baoquan He <b...@redhat.com> Acked-by: Xunlei Pang <xp...@redhat.com> --- Documentation/kdump/kdump.txt | 7 +++ 1 file changed, 7 insertions(+) diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt index d900080..31e6b88 100644 --- a/Documentation/kdump/kdump.txt +++ b/Documentation/kdump/kdump.txt @@ -396,6 +396,13 @@ Notes on loading the dump-capture kernel: Note, though maxcpus always works, you should replace it by nr_cpus to save memory if supported by the current ARCH, such as x86. +* You should enable multi-cpu support in dump-capture kernel if you intend + to use multi-thread programs with it, such as parallel dump feature of + makedumpfile. Otherwise, the multi-thread program may have a great + performance degradation. To enable multi-cpu support, you should bring up an + SMP dump-capture kernel and specify maxcpus/nr_cpus, disable_cpu_apicid=[X] + options while loading it. + * For s390x there are two kdump modes: If a ELF header is specified with the elfcorehdr= kernel parameter, it is used by the kdump kernel as it is done on all other architectures. If no elfcorehdr= kernel parameter is -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH v8 1/2] Documentation: kdump: remind user of nr_cpus
nr_cpus can help to save memory. So we should remind user of it. Signed-off-by: Zhou Wenjian <zhouwj-f...@cn.fujitsu.com> Acked-by: Baoquan He <b...@redhat.com> Acked-by: Xunlei Pang <xp...@redhat.com> --- Documentation/kdump/kdump.txt | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt index 88ff63d..e8da1d5 100644 --- a/Documentation/kdump/kdump.txt +++ b/Documentation/kdump/kdump.txt @@ -390,9 +390,11 @@ Notes on loading the dump-capture kernel: * Boot parameter "1" boots the dump-capture kernel into single-user mode without networking. If you want networking, use "3". -* We generally don' have to bring up a SMP kernel just to capture the +* We generally don' have to bring up an SMP kernel just to capture the dump. Hence generally it is useful either to build a UP dump-capture kernel or specify maxcpus=1 option while loading dump-capture kernel. + Note, though maxcpus always works, you should replace it by nr_cpus to + save memory if supported by the current ARCH, such as x86. * For s390x there are two kdump modes: If a ELF header is specified with the elfcorehdr= kernel parameter, it is used by the kdump kernel as it -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH v8 0/2] update the doc of kdump
v7->v8: fix "a SMP kernel" to "an SMP kernel" and replace "\" with "/" v6->v7: fix typo v5->v6: replace "we" with "you" v4->v5: move change log to cover letter v3->v4: update the description of bring up SMP dump-capture kernel v2->v3: add description of nr_cpus. v1->v2: change nr_cpus to maxcpus Zhou Wenjian (2): Documentation: kdump: remind user of nr_cpus Documentation: kdump: add description of enable multi-cpus support Documentation/kdump/kdump.txt | 11 ++- 1 file changed, 10 insertions(+), 1 deletion(-) -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH v8 2/2] Documentation: kdump: add description of enable multi-cpus support
multi-cpu support is useful to improve the performance of kdump in some cases. So add the description of enable multi-cpu support in dump-capture kernel. Signed-off-by: Zhou Wenjian <zhouwj-f...@cn.fujitsu.com> Acked-by: Baoquan He <b...@redhat.com> Acked-by: Xunlei Pang <xp...@redhat.com> --- Documentation/kdump/kdump.txt | 7 +++ 1 file changed, 7 insertions(+) diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt index e8da1d5..c781d49 100644 --- a/Documentation/kdump/kdump.txt +++ b/Documentation/kdump/kdump.txt @@ -396,6 +396,13 @@ Notes on loading the dump-capture kernel: Note, though maxcpus always works, you should replace it by nr_cpus to save memory if supported by the current ARCH, such as x86. +* You should enable multi-cpu support in dump-capture kernel if you intend + to use multi-thread programs with it, such as parallel dump feature of + makedumpfile. Otherwise, the multi-thread program may have a great + performance degradation. To enable multi-cpu support, you should bring up an + SMP dump-capture kernel and specify maxcpus/nr_cpus, disable_cpu_apicid=[X] + options while loading it. + * For s390x there are two kdump modes: If a ELF header is specified with the elfcorehdr= kernel parameter, it is used by the kdump kernel as it is done on all other architectures. If no elfcorehdr= kernel parameter is -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH v7 0/2] update the doc of kdump
v6->v7: fix typo v5->v6: replace "we" with "you" v4->v5: move change log to cover letter v3->v4: update the description of bring up SMP dump-capture kernel v2->v3: add description of nr_cpus. v1->v2: change nr_cpus to maxcpus Zhou Wenjian (2): Documentation: kdump: remind user of nr_cpus Documentation: kdump: add description of enable multi-cpus support Documentation/kdump/kdump.txt | 11 ++- 1 file changed, 10 insertions(+), 1 deletion(-) -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH v7 1/2] Documentation: kdump: remind user of nr_cpus
nr_cpus can help to save memory. So we should remind user of it. Signed-off-by: Zhou Wenjian <zhouwj-f...@cn.fujitsu.com> Acked-by: Baoquan He <b...@redhat.com> --- Documentation/kdump/kdump.txt | 2 +++- 1 file changed, 2 insertions(+) diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt index 88ff63d..96da2b7 100644 --- a/Documentation/kdump/kdump.txt +++ b/Documentation/kdump/kdump.txt @@ -393,6 +393,8 @@ Notes on loading the dump-capture kernel: * We generally don' have to bring up a SMP kernel just to capture the dump. Hence generally it is useful either to build a UP dump-capture kernel or specify maxcpus=1 option while loading dump-capture kernel. + Note, though maxcpus always works, you should replace it by nr_cpus to + save memory if supported by the current ARCH, such as x86. * For s390x there are two kdump modes: If a ELF header is specified with the elfcorehdr= kernel parameter, it is used by the kdump kernel as it -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH v7 2/2] Documentation: kdump: add description of enable multi-cpus support
multi-cpu support is useful to improve the performance of kdump in some cases. So add the description of enable multi-cpu support in dump-capture kernel. Signed-off-by: Zhou Wenjian <zhouwj-f...@cn.fujitsu.com> Acked-by: Baoquan He <b...@redhat.com> --- Documentation/kdump/kdump.txt | 7 +++ 1 file changed, 7 insertions(+) diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt index 96da2b7..c93a6e0 100644 --- a/Documentation/kdump/kdump.txt +++ b/Documentation/kdump/kdump.txt @@ -396,6 +396,13 @@ Notes on loading the dump-capture kernel: Note, though maxcpus always works, you should replace it by nr_cpus to save memory if supported by the current ARCH, such as x86. +* You should enable multi-cpu support in dump-capture kernel if you intend + to use multi-thread programs with it, such as parallel dump feature of + makedumpfile. Otherwise, the multi-thread program may have a great + performance degradation. To enable multi-cpu support, you should bring up + a SMP dump-capture kernel and specify maxcpus\nr_cpus, disable_cpu_apicid=[X] + options while loading it. + * For s390x there are two kdump modes: If a ELF header is specified with the elfcorehdr= kernel parameter, it is used by the kdump kernel as it is done on all other architectures. If no elfcorehdr= kernel parameter is -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH v6 2/2] Documentation: kdump: add description of enable multi-cpus support
multi-cpu support is useful to improve the performance of kdump in some cases. So add the description of enable multi-cpu support in dump-capture kernel. Signed-off-by: Zhou Wenjian <zhouwj-f...@cn.fujitsu.com> Acked-by: Baoquan He <b...@redhat.com> --- Documentation/kdump/kdump.txt | 7 +++ 1 file changed, 7 insertions(+) diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt index 96da2b7..c93a6e0 100644 --- a/Documentation/kdump/kdump.txt +++ b/Documentation/kdump/kdump.txt @@ -396,6 +396,13 @@ Notes on loading the dump-capture kernel: Note, though maxcpus always works, you should replace it by nr_cpus to save memory if supported by the current ARCH, such as x86. +* You should enable multi-cpu support in dump-capture kernel if you intend + to use multi-thread programs with it, such as parallel dump feature of + makedumpfile. Otherwise, the multi-thread program may have a great + performance degradation. To enable multi-cpu support, you should bring up + a SMP dump-capture kernel and specify maxcpus\nr_cpus, disable_cpu_apic=[X] + options while loading it. + * For s390x there are two kdump modes: If a ELF header is specified with the elfcorehdr= kernel parameter, it is used by the kdump kernel as it is done on all other architectures. If no elfcorehdr= kernel parameter is -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH v6 0/2] update the doc of kdump
v5->v6: replace "we" with "you" v4->v5: move change log to cover letter v3->v4: update the description of bring up SMP dump-capture kernel v2->v3: add description of nr_cpus. v1->v2: change nr_cpus to maxcpus Zhou Wenjian (2): Documentation: kdump: remind user of nr_cpus Documentation: kdump: add description of enable multi-cpus support Documentation/kdump/kdump.txt | 11 ++- 1 file changed, 10 insertions(+), 1 deletion(-) -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
