Re: [dm-devel] 答复: Re: [PATCH] multipath-tools: improve processing efficiency for addition and deletion of multipath devices
On Fri, Feb 17, 2017 at 11:24:10AM +0800, tang.jun...@zte.com.cn wrote:
>Hello Martin,
>
>Thanks for your responsible,
>
>＞ I'd like the following better for this check. It uses much less cycles.
>
>＞ static bool
>＞ can_discard_by_devpath(const char *devpath)
>
>＞ This would be better readable and faster if you'd put the "kernel"
>＞ tests first so that you need to check only "action" later:
>
>＞ if (!strncmp(later-＞kernel, "dm-", 3) ||
>＞ strcmp(earlier-＞kernel, later-＞kernel))
>＞return false;
>
>Yes, I think these codes can be reworked, but since they have no logical
>
>effect, and this patch takes too long time, can you commit a new patch
>
>to rework these codes?
>
>＞ The first case should have been reduced to "remove path1 | remove path2
>
>＞ | add path3" by filtering beforehand. I suppose you want to avoid this
>
>＞ sequence because it could leave us without paths temporarily, causing
>
>＞ multipathd to destroy the map. But I don't understand what "stop
>
>＞ merging" buys you here - if you process the events one-by-one, you may
>
>＞ also have 0 paths at some point.
>
>＞
>
>＞ In the second case, we know all events in the sequence have the same
>
>＞ WWID; in this case I think it would be safe to filter away "remove"
>
>＞ events by subsequent "add" events, ending up with "add path1| add
>
>＞ path2| remove path3". But I may be overlooking something here.
>
>＞ The dangerous thing if you have simultaneous remove and add events for
>
>＞ the same LUN is that processing the "add" events is likely to fail in
>
>＞ domap(). If you get "add path1 | remove path2", once you process "add
>
>＞ path1", "path2" may not exist in the kernel any more, and "domap" will
>
>＞ fail if you try to set up both; you may end up removing the map
>
>＞ completely. IMHO the only safe way to process events in this situation
>
>＞ is to merge the events into a single domap() call.
>
>"case 2: remove path1 |add path1 |remove path2 |add path2 |remove path3"
>
>Since the mergering is starting from the latest to the eariest uevent, so
>the
>
>uevent "remove path3" try to merger other uevents, if we do not stop
>mergering,
>
>uevent "remove path3" would merge uevent "remove path2" and uevent
>
>"remove path1". Uevent "add path2" would merge "add path1".
>
>The result is that we get two merged uevents:
>
>1) add path2, path1
>
>2) remove path3, path2, path1
>
>Then we process the merged uevents from the earlier to later, We try to
>”add
>
>path2 path1“, and we would create or reload a map device with path1 and
>path2.
>
>Next we process ” remove path3, path2, path1“, so path1, path2 and path3
>are
>
>all removed from the map device, this is wrong, the correct result is
>that the path1
>
>and path2 should be still in the map device.
>
>Just as you say, this patch is just a shape, we need more testing, and
>maybe
>
>more patches are needed to make it better.
But in theory, you could have one merged uevent where you
remove path1, add path1, remove path2, add path2, remove path3, and then
call domap one time.
As long as you keep them in right order, I think you could just merge
add and remove events. But what you have right now handles the common
cases, which are bursts of add/chage events, and bursts of remove events.
-Ben
>
>Thank you,
>
>Tang Junhui
>
>
>
> 原始邮件
>发件人： ＜mwi...@suse.com＞;
>收件人：唐军辉10074136; ＜christophe.varo...@opensvc.com＞;
>＜bmarz...@redhat.com＞; ＜h...@suse.de＞; ＜bart.vanass...@sandisk.com＞;
>抄送人：张凯10072500; ＜dm-devel@redhat.com＞;唐文俊10144149;
>日 期 ：2017年02月17日 05:22
>主 题 ：Re: [dm-devel] [PATCH] multipath-tools: improve processing
>efficiency for addition and deletion of multipath devices
>
>Hello Tang,
>
>I'm sorry to reply so late. Thanks a lot for your work, I agree with
>Ben that the patch is in pretty good shape now. But I have some
>remarks left, please see below.
>
>＞ +bool
>＞ +uevent_can_discard(struct uevent *uev)
>＞ +{
>＞ +char *tmp;
>＞ +char a[11], b[11];
>＞ +struct config * conf;
>＞ +
>＞ +/*
>＞ + * keep only block devices, discard partitions
>＞ + */
>＞ +tmp = strstr(uev-＞devpath, "/block/");
>＞ +if (tmp == NULL){
>＞ +condlog(4, "no /block/ in '%s'", uev-＞devpath);
>＞ +return true;
>＞ +}
>＞ +if (sscanf(tmp, "/block/%10s", a) != 1 ||
>＞ +sscanf(tmp, "/block/%10[^/]/%10s", a, b) == 2) {
>＞ +condlog(4, "discard event on %s", uev-＞devpath);
>＞ +return true;
>＞ +}
>
>I'd like the following better for this check. It uses much less cycles.
>
>static bool
>can_di
Re: [dm-devel] 答复: Re: [PATCH] multipath-tools: improve processing efficiency for addition and deletion of multipath devices
On Fri, 2017-02-17 at 11:24 +0800, tang.jun...@zte.com.cn wrote: > Hello Martin, > > Thanks for your responsible, > > ＞ I'd like the following better for this check. It uses much less cyc > les. > > ＞ static bool > ＞ can_discard_by_devpath(const char *devpath) > > ＞ This would be better readable and faster if you'd put the "kernel" > ＞ tests first so that you need to check only "action" later: > > ＞ if (!strncmp(later-＞kernel, "dm-", 3) || > ＞ strcmp(earlier-＞kernel, later-＞kernel)) > ＞return false; > > Yes, I think these codes can be reworked, but since they have no > logical > effect, and this patch takes too long time, can you commit a new > patch > to rework these codes? Yes, I could do that. Regards Martin -- Dr. Martin Wilck , Tel. +49 (0)911 74053 2107 SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton HRB 21284 (AG Nürnberg) -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel
Re: [dm-devel] 答复: Re: [PATCH] multipath-tools: improve processing efficiency for addition and deletion of multipath devices
Hello Tang, ＞ In the second case, we know all events in the sequence have the > same > ＞ WWID; in this case I think it would be safe to filter away "remove" > ＞ events by subsequent "add" events, ending up with "add path1| add > ＞ path2| remove path3". But I may be overlooking something here. > > ＞ The dangerous thing if you have simultaneous remove and add events > for > ＞ the same LUN is that processing the "add" events is likely to fail > in > ＞ domap(). If you get "add path1 | remove path2", once you process > "add > ＞ path1", "path2" may not exist in the kernel any more, and "domap" > will > ＞ fail if you try to set up both; you may end up removing the map > ＞ completely. IMHO the only safe way to process events in this > situation > ＞ is to merge the events into a single domap() call. > > "case 2: remove path1 |add path1 |remove path2 |add path2 |remove > path3" > Since the mergering is starting from the latest to the eariest > uevent, so the > uevent "remove path3" try to merger other uevents, if we do not stop > mergering, > uevent "remove path3" would merge uevent "remove path2" and uevent > "remove path1". Uevent "add path2" would merge "add path1". > The result is that we get two merged uevents: > 1) add path2, path1 > 2) remove path3, path2, path1 > Then we process the merged uevents from the earlier to later, We try > to ”add > path2 path1“, and we would create or reload a map device with path1 > and path2. > Next we process ” remove path3, path2, path1“, so path1, path2 and > path3 are > all removed from the map device, this is wrong, the correct result > is that the path1 > and path2 should be still in the map device. I don't understand that. This would mean that you'd re-order "remove path1 | add path1" into "add path1| remove path1", and the same for path2. That may obviously never happen. Your "stop merging" logic forbids it, and that's fine for me for now. Regards Martin -- Dr. Martin Wilck , Tel. +49 (0)911 74053 2107 SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton HRB 21284 (AG Nürnberg) -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel
Re: [dm-devel] 答复: Re: [PATCH] multipath-tools: improve processing efficiency for addition and deletion of multipath devices
Hello Martin, This exmaple shows why we need to stop merging, Yes, It's fine since we have "stop merging" in current code. RegardsTang 原始邮件 发件人： ＜mwi...@suse.com＞ 收件人： ＜dm-devel@redhat.com＞ 日 期 ：2017年02月20日 19:24 主 题 ：Re: [dm-devel] 答复: Re: [PATCH] multipath-tools: improve processing efficiency for addition and deletion of multipath devices Hello Tang, ＞ In the second case, we know all events in the sequence have the ＞ same ＞ ＞ WWID in this case I think it would be safe to filter away "remove" ＞ ＞ events by subsequent "add" events, ending up with "add path1| add ＞ ＞ path2| remove path3". But I may be overlooking something here. ＞ ＞ ＞ The dangerous thing if you have simultaneous remove and add events ＞ for ＞ ＞ the same LUN is that processing the "add" events is likely to fail ＞ in ＞ ＞ domap(). If you get "add path1 | remove path2", once you process ＞ "add ＞ ＞ path1", "path2" may not exist in the kernel any more, and "domap" ＞ will ＞ ＞ fail if you try to set up both you may end up removing the map ＞ ＞ completely. IMHO the only safe way to process events in this ＞ situation ＞ ＞ is to merge the events into a single domap() call. ＞ ＞ "case 2: remove path1 |add path1 |remove path2 |add path2 |remove ＞ path3" ＞ Since the mergering is starting from the latest to the eariest ＞ uevent, so the ＞ uevent "remove path3" try to merger other uevents, if we do not stop ＞ mergering, ＞ uevent "remove path3" would merge uevent "remove path2" and uevent ＞ "remove path1". Uevent "add path2" would merge "add path1". ＞ The result is that we get two merged uevents: ＞ 1) add path2, path1 ＞ 2) remove path3, path2, path1 ＞ Then we process the merged uevents from the earlier to later, We try ＞ to ”add ＞ path2 path1“, and we would create or reload a map device with path1 ＞ and path2. ＞ Next we process ” remove path3, path2, path1“, so path1, path2 and ＞ path3 are ＞ all removed from the map device, this is wrong, the correct result ＞ is that the path1 ＞ and path2 should be still in the map device. I don't understand that. This would mean that you'd re-order "remove path1 | add path1" into "add path1| remove path1", and the same for path2. That may obviously never happen. Your "stop merging" logic forbids it, and that's fine for me for now. Regards Martin -- Dr. Martin Wilck ＜mwi...@suse.com＞, Tel. +49 (0)911 74053 2107 SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton HRB 21284 (AG Nürnberg) -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel-- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel
