Does WSP deployment triggers IISRESET?
Depends on type of deployment. There are 2 kinds: Local and Timer Service deployments
(Deploying a Solution). BE AWARE that WSP solution retractions causes IISRESET too.
Local WSP deployment - stsadm -o deploysolution -local .Deploys the solution synchronously on the local computer only. The timer service is not used. . It will call IISRESET but locally on the WFE, not in all WFEs in the farm.
Farm solution deployment with no downtime. Update-SPSolution -local
Timer Service Deployment - stsadm -o deploysolution -immeidate (or -time)
(Deploysolution: Stsadm operation) . Uses a timer job and triggers IISRESET.
The deployment step for a farm solution creates a timer job. This timer job is used by the timer service on each web server in the server farm. The timer job also uses the SharePoint Foundation Administrative web service to access appropriate privileges to deploy solution files to each computer, so both services must be running on all servers for the deployment to succeed.
More detail coverage on the topic: SharePoint Solution Deploy, retract, upgrade – What causes your SharePoint farm to go offline IISRESET (web server outage).