From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Grover Subject: Re: dm-delay: Add a message to change delay Date: Tue, 1 Sep 2015 07:17:46 -0700 Message-ID: <55E5B38A.4020101@redhat.com> References: <1441056276-14288-1-git-send-email-agrover@redhat.com> <20150901020557.GA31620@redhat.com> <55E53169.1030105@redhat.com> <20150901121427.GA2906@redhat.com> <20150901130934.GA14882@redhat.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150901130934.GA14882@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Mike Snitzer , Vivek Goyal Cc: dm-devel@redhat.com List-Id: dm-devel.ids On 09/01/2015 06:09 AM, Mike Snitzer wrote: > On Tue, Sep 01 2015 at 8:14am -0400, > Vivek Goyal wrote: > >> On Mon, Aug 31, 2015 at 10:02:33PM -0700, Andy Grover wrote: >>> On 08/31/2015 07:05 PM, Vivek Goyal wrote: >>>> On Mon, Aug 31, 2015 at 02:24:36PM -0700, Andy Grover wrote: >>>>> This enables runtime modification of the read and write delay values. >>>>> >>>>> Make sure if the delay time is reduced to flush currently-delayed >>>>> bios first, to maintain ordering. >>>>> >>>>> Signed-off-by: Andy Grover >>>>> --- >>>>> Documentation/device-mapper/delay.txt | 8 +++++++ >>>>> drivers/md/dm-delay.c | 42 +++++++++++++++++++++++++++++++++++ >>>>> 2 files changed, 50 insertions(+) >>>>> >>>>> diff --git a/Documentation/device-mapper/delay.txt b/Documentation/device-mapper/delay.txt >>>>> index 15adc55..9e80751 100644 >>>>> --- a/Documentation/device-mapper/delay.txt >>>>> +++ b/Documentation/device-mapper/delay.txt >>>>> @@ -10,6 +10,14 @@ Parameters: >>>>> With separate write parameters, the first set is only used for reads. >>>>> Delays are specified in milliseconds. >>>>> >>>>> +Message Interface >>>>> +----------------- >>>>> +The delay target will accept a message of the following format: >>>>> + >>>>> +set_delay [] >>>>> + >>>> >>>> Hi Andy, >>>> >>>> So if I want to change only write_delay and keep read_delay same, how do >>>> I do that. Do I have to keep track of existing delay values in user space >>>> and pass same value in read_delay to achieve this. >>>> >>>> Thanks >>>> Vivek >>> >>> Hi Vivek, >>> >>> Yes I suppose userspace would either need to remember read_delay so as to >>> not change it while setting write_delay, or I guess it could read the >>> existing values by getting table status before sending the message. Is this >>> reasonable, or do you think it would be better to, say, have separate >>> messages for setting the two values, or some other message style? >> >> Ideally I think we should have those --key=value type of arguments which >> we don't have yet. So that option is not feasible I guess. >> >> If latest values are readable from status, then I think single message >> sounds reasoanble to me. > > As Zdenek already effectively said: there is no need for this patch. > You don't need to use a message when a table reload would suffice to > change the parameter that is already passed on the table ctr. > > Any layer that would be trained to send a message can just as easily be > trained to reload the table to achieve the same result. Ah I see. Thanks for the explanations. Noflush suspend & table reload is better for this. Regards -- Andy