From 555ebc2e544437445450239b48e7df9b4f371460 Mon Sep 17 00:00:00 2001
From: Bruno Donassolo <bruno.donassolo@inria.fr>
Date: Tue, 27 Jul 2021 10:23:30 +0200
Subject: [PATCH] I/O factors: noise for disks.

Implements variability in disk operations.
Similarly to network factors, the effective amount of bytes read/written
in disk operations is scaled by a factor defined by the user.

Users can define a different callback for each disk. The callback is
called when SimGrid updates the remaining amount of bytes in disk
operations.
---
 include/simgrid/s4u/Disk.hpp     | 12 ++++++++++++
 src/kernel/activity/IoImpl.cpp   |  4 ++++
 src/kernel/resource/DiskImpl.cpp |  6 ++++++
 src/kernel/resource/DiskImpl.hpp |  4 ++++
 src/s4u/s4u_Disk.cpp             |  6 ++++++
 5 files changed, 32 insertions(+)

diff --git a/include/simgrid/s4u/Disk.hpp b/include/simgrid/s4u/Disk.hpp
index fcd8a651ab..5ba6306774 100644
--- a/include/simgrid/s4u/Disk.hpp
+++ b/include/simgrid/s4u/Disk.hpp
@@ -96,6 +96,18 @@ public:
    */
   Disk* set_sharing_policy(Operation op, SharingPolicy policy, const s4u::NonLinearResourceCb& cb = {});
   SharingPolicy get_sharing_policy(Operation op) const;
+  /**
+   * @brief Callback to set IO factors
+   *
+   * This callback offers a flexible way to create variability in I/O operations
+   *
+   * @param size I/O operation size in bytes
+   * @param op I/O operation type: read or write
+   * @return Multiply factor
+   */
+  using IoFactorCb = double(sg_size_t size, Io::OpType op);
+  /** @brief Configure the factor callback */
+  Disk* set_factor_cb(const std::function<IoFactorCb>& cb);
 
   Disk* seal();
 
diff --git a/src/kernel/activity/IoImpl.cpp b/src/kernel/activity/IoImpl.cpp
index 4f692b2990..bdef78f4d7 100644
--- a/src/kernel/activity/IoImpl.cpp
+++ b/src/kernel/activity/IoImpl.cpp
@@ -59,6 +59,10 @@ IoImpl* IoImpl::start()
   surf_action_ =
       disk_->get_host()->get_netpoint()->get_englobing_zone()->get_disk_model()->io_start(disk_, size_, type_);
   surf_action_->set_activity(this);
+  const auto& factor_cb = disk_->get_factor_cb();
+  if (factor_cb) { // handling disk variability
+    surf_action_->set_rate_factor(factor_cb(size_, type_));
+  }
 
   XBT_DEBUG("Create IO synchro %p %s", this, get_cname());
 
diff --git a/src/kernel/resource/DiskImpl.cpp b/src/kernel/resource/DiskImpl.cpp
index dc0944946f..7b1fca1b4c 100644
--- a/src/kernel/resource/DiskImpl.cpp
+++ b/src/kernel/resource/DiskImpl.cpp
@@ -156,6 +156,12 @@ void DiskImpl::apply_sharing_policy_cfg()
                                           sharing_policy_cb_[s4u::Disk::Operation::WRITE]);
 }
 
+void DiskImpl::set_factor_cb(const std::function<s4u::Disk::IoFactorCb>& cb)
+{
+  xbt_assert(not is_sealed(), "Cannot set I/O factor callback in an already sealed disk(%s)", get_cname());
+  factor_cb_ = cb;
+}
+
 /**********
  * Action *
  **********/
diff --git a/src/kernel/resource/DiskImpl.hpp b/src/kernel/resource/DiskImpl.hpp
index c7835b6fc9..80905f909e 100644
--- a/src/kernel/resource/DiskImpl.hpp
+++ b/src/kernel/resource/DiskImpl.hpp
@@ -56,6 +56,7 @@ class DiskImpl : public Resource_T<DiskImpl>, public xbt::PropertyHolder {
       {s4u::Disk::Operation::WRITE, s4u::Disk::SharingPolicy::LINEAR},
       {s4u::Disk::Operation::READWRITE, s4u::Disk::SharingPolicy::LINEAR}};
   std::unordered_map<s4u::Disk::Operation, s4u::NonLinearResourceCb> sharing_policy_cb_ = {};
+  std::function<s4u::Disk::IoFactorCb> factor_cb_                                       = {};
 
   void apply_sharing_policy_cfg();
 
@@ -94,6 +95,9 @@ public:
   void set_sharing_policy(s4u::Disk::Operation op, s4u::Disk::SharingPolicy policy, const s4u::NonLinearResourceCb& cb);
   s4u::Disk::SharingPolicy get_sharing_policy(s4u::Disk::Operation op) const;
 
+  void set_factor_cb(const std::function<s4u::Disk::IoFactorCb>& cb);
+  const std::function<s4u::Disk::IoFactorCb>& get_factor_cb() const { return factor_cb_; }
+
   /** @brief Check if the Disk is used (if an action currently uses its resources) */
   bool is_used() const override;
   void turn_on() override;
diff --git a/src/s4u/s4u_Disk.cpp b/src/s4u/s4u_Disk.cpp
index 29adfd31d4..d3f3a46100 100644
--- a/src/s4u/s4u_Disk.cpp
+++ b/src/s4u/s4u_Disk.cpp
@@ -142,6 +142,12 @@ Disk::SharingPolicy Disk::get_sharing_policy(Operation op) const
   return this->pimpl_->get_sharing_policy(op);
 }
 
+Disk* Disk::set_factor_cb(const std::function<IoFactorCb>& cb)
+{
+  kernel::actor::simcall([this, &cb] { pimpl_->set_factor_cb(cb); });
+  return this;
+}
+
 Disk* Disk::seal()
 {
   kernel::actor::simcall([this]{ pimpl_->seal(); });
-- 
2.20.1