diff --git a/dnn/src/arm_common/pooling/opr_impl.cpp b/dnn/src/arm_common/pooling/opr_impl.cpp
index 6e121863..6e33a7f6 100644
--- a/dnn/src/arm_common/pooling/opr_impl.cpp
+++ b/dnn/src/arm_common/pooling/opr_impl.cpp
@@ -51,15 +51,6 @@ PoolingImpl::AlgoPack PoolingImpl::sm_algo_pack;
 
 size_t PoolingImpl::get_workspace_in_bytes(
         const TensorLayout& src, const TensorLayout& dst) {
-    TensorLayoutArray layouts{src, dst};
-    AlgorithmCache::Key key{this->handle(), this->get_opr_type(),
-                            layouts.data(), layouts.size(),
-                            &this->param(), sizeof(this->param())};
-    auto rst = AlgorithmCache::instance().get(key);
-    if (rst.policy.algo.valid()) {
-        return rst.workspace;
-    }
-
     auto param = make_pooling_kern_szie_param(this, src, dst);
     auto algo = get_algorithm(this, src, dst);
     if (!is_fallback_algo(algo)) {
diff --git a/dnn/src/common/algo_chooser.h b/dnn/src/common/algo_chooser.h
index 824e6c3a..23be68de 100644
--- a/dnn/src/common/algo_chooser.h
+++ b/dnn/src/common/algo_chooser.h
@@ -13,14 +13,6 @@ namespace megdnn {
 
 template <class Opr, typename... Args>
 size_t get_dnn_workspace(Opr* opr, Args&&... args) {
-    TensorLayoutArray layouts{{args...}};
-    AlgorithmCache::Key key{opr->handle(),  opr->get_opr_type(), layouts.data(),
-                            layouts.size(), &opr->param(),       sizeof(opr->param())};
-    auto rst = AlgorithmCache::instance().get(key);
-    if (rst.policy.algo.valid()) {
-        return rst.workspace;
-    }
-
     typename Opr::AlgoBase::SizeArgs size_args(opr, std::forward<Args>(args)...);
     return get_algorithm(opr, std::forward<Args>(args)...)
             ->get_workspace_in_bytes(size_args);
@@ -32,6 +24,7 @@ size_t get_dnn_workspace(Opr* opr, Args&&... args) {
 template <class Opr, typename... Args>
 typename Opr::AlgoBase* get_algorithm(Opr* opr, Args&&... args) {
     typename Opr::AlgorithmDesc ret;
+    // first check self configured algorithm
     auto set = opr->execution_policy().algo;
     if (set.valid()) {
         ret = set;
@@ -40,10 +33,12 @@ typename Opr::AlgoBase* get_algorithm(Opr* opr, Args&&... args) {
         AlgorithmCache::Key key{opr->handle(),  opr->get_opr_type(),
                                 layouts.data(), layouts.size(),
                                 &opr->param(),  sizeof(opr->param())};
+        // then get from global algorithm cache
         auto rst = AlgorithmCache::instance().get(key);
         if (rst.policy.algo.valid()) {
             ret = rst.policy.algo;
         } else {
+            // finally get pre-defined heuristic algorithm
             ret = opr->get_algorithm_info_heuristic(
                              std::forward<Args>(args)...,
                              std::numeric_limits<size_t>::max(), AlgoAttribute::DEFAULT,
diff --git a/dnn/src/naive/batch_conv_bias/opr_impl.cpp b/dnn/src/naive/batch_conv_bias/opr_impl.cpp
index c0c8edeb..fe86bd7d 100644
--- a/dnn/src/naive/batch_conv_bias/opr_impl.cpp
+++ b/dnn/src/naive/batch_conv_bias/opr_impl.cpp
@@ -44,14 +44,6 @@ WorkspaceBundle BatchConvBiasForwardImpl::get_workspace_bundle(
 size_t BatchConvBiasForwardImpl::get_workspace_in_bytes(
         const TensorLayout& src, const TensorLayout& flt, const TensorLayout& bias,
         const TensorLayout& z, const TensorLayout& dst) {
-    TensorLayoutArray layouts{src, flt, bias, z, dst};
-    AlgorithmCache::Key key{this->handle(), this->get_opr_type(),
-                            layouts.data(), layouts.size(),
-                            &this->param(), sizeof(this->param())};
-    auto rst = AlgorithmCache::instance().get(key);
-    if (rst.policy.algo.valid()) {
-        return rst.workspace;
-    }
     return get_workspace_bundle(nullptr, src, flt, bias, z, dst).total_size_in_bytes();
 }
 
diff --git a/dnn/src/naive/conv_bias/opr_impl.cpp b/dnn/src/naive/conv_bias/opr_impl.cpp
index d940b227..56157578 100644
--- a/dnn/src/naive/conv_bias/opr_impl.cpp
+++ b/dnn/src/naive/conv_bias/opr_impl.cpp
@@ -187,15 +187,6 @@ void forward_bias<dt_quint4, dt_qint4, dt_qint32, dt_qint32>(
 size_t ConvBiasForwardImpl::get_workspace_in_bytes(
         const TensorLayout& src, const TensorLayout& flt, const TensorLayout& bias,
         const TensorLayout& z, const TensorLayout& dst, const PreprocessedFilter*) {
-    TensorLayoutArray layouts{src, flt, bias, z, dst};
-    AlgorithmCache::Key key{this->handle(), this->get_opr_type(),
-                            layouts.data(), layouts.size(),
-                            &this->param(), sizeof(this->param())};
-    auto rst = AlgorithmCache::instance().get(key);
-    if (rst.policy.algo.valid()) {
-        return rst.workspace;
-    }
-
     size_t float_workspace_size = 0;
 
     if (z.ndim > 0 && z.dtype.category() != DTypeCategory::FLOAT) {
diff --git a/dnn/src/naive/convolution/opr_impl.cpp b/dnn/src/naive/convolution/opr_impl.cpp
index 15b50c86..e860bd5e 100644
--- a/dnn/src/naive/convolution/opr_impl.cpp
+++ b/dnn/src/naive/convolution/opr_impl.cpp
@@ -66,15 +66,6 @@ void ConvolutionForwardImpl::exec(
 size_t ConvolutionBackwardDataImpl::get_workspace_in_bytes(
         const TensorLayout& filter, const TensorLayout& diff,
         const TensorLayout& grad) {
-    TensorLayoutArray layouts{filter, diff, grad};
-    AlgorithmCache::Key key{this->handle(), this->get_opr_type(),
-                            layouts.data(), layouts.size(),
-                            &this->param(), sizeof(this->param())};
-    auto rst = AlgorithmCache::instance().get(key);
-    if (rst.policy.algo.valid()) {
-        return rst.workspace;
-    }
-
     size_t workspace_size = 0;
     auto flt_dt = filter.dtype.enumv();
     auto grad_dt = grad.dtype.enumv();
@@ -178,15 +169,6 @@ size_t ConvolutionBackwardFilterImpl::get_workspace_in_bytes(
         const TensorLayout& src, const TensorLayout& diff, const TensorLayout& grad) {
     size_t workspace_size = 0;
 #if !MEGDNN_DISABLE_FLOAT16
-    TensorLayoutArray layouts{src, diff, grad};
-    AlgorithmCache::Key key{this->handle(), this->get_opr_type(),
-                            layouts.data(), layouts.size(),
-                            &this->param(), sizeof(this->param())};
-    auto rst = AlgorithmCache::instance().get(key);
-    if (rst.policy.algo.valid()) {
-        return rst.workspace;
-    }
-
     auto src_dt = src.dtype.enumv();
     auto grad_dt = grad.dtype.enumv();
     auto diff_dt = diff.dtype.enumv();
diff --git a/dnn/src/naive/pooling/opr_impl.cpp b/dnn/src/naive/pooling/opr_impl.cpp
index 96917394..0b5c1f8b 100644
--- a/dnn/src/naive/pooling/opr_impl.cpp
+++ b/dnn/src/naive/pooling/opr_impl.cpp
@@ -397,14 +397,6 @@ WorkspaceBundle PoolingForwardImpl::get_workspace_bundle(
 
 size_t PoolingForwardImpl::get_workspace_in_bytes(
         const TensorLayout& src, const TensorLayout& dst) {
-    TensorLayoutArray layouts{src, dst};
-    AlgorithmCache::Key key{this->handle(), this->get_opr_type(),
-                            layouts.data(), layouts.size(),
-                            &this->param(), sizeof(this->param())};
-    auto rst = AlgorithmCache::instance().get(key);
-    if (rst.policy.algo.valid()) {
-        return rst.workspace;
-    }
     return get_workspace_bundle(nullptr, src, dst).total_size_in_bytes();
 }
 namespace {
@@ -649,14 +641,6 @@ WorkspaceBundle PoolingBackwardImpl::get_workspace_bundle(
 size_t PoolingBackwardImpl::get_workspace_in_bytes(
         const TensorLayout& src, const TensorLayout& dst, const TensorLayout& diff,
         const TensorLayout& grad) {
-    TensorLayoutArray layouts{src, dst, diff, grad};
-    AlgorithmCache::Key key{this->handle(), this->get_opr_type(),
-                            layouts.data(), layouts.size(),
-                            &this->param(), sizeof(this->param())};
-    auto rst = AlgorithmCache::instance().get(key);
-    if (rst.policy.algo.valid()) {
-        return rst.workspace;
-    }
     return get_workspace_bundle(nullptr, src, dst, diff, grad).total_size_in_bytes();
 }
 
diff --git a/dnn/src/rocm/convolution/opr_impl.cpp b/dnn/src/rocm/convolution/opr_impl.cpp
index 8c88b130..1d909ffd 100644
--- a/dnn/src/rocm/convolution/opr_impl.cpp
+++ b/dnn/src/rocm/convolution/opr_impl.cpp
@@ -104,15 +104,6 @@ std::vector<ConvolutionForwardImpl::Algorithm*> ConvolutionForwardImpl::
 size_t ConvolutionForwardImpl::get_workspace_in_bytes(
         const TensorLayout& src, const TensorLayout& filter, const TensorLayout& dst,
         const PreprocessedFilter*) {
-    TensorLayoutArray layouts{src, filter, dst};
-    AlgorithmCache::Key key{this->handle(), this->get_opr_type(),
-                            layouts.data(), layouts.size(),
-                            &this->param(), sizeof(this->param())};
-    auto rst = AlgorithmCache::instance().get(key);
-    if (rst.policy.algo.valid()) {
-        return rst.workspace;
-    }
-
     AlgoBase::SizeArgs args(this, src, filter, dst);
     return get_algorithm(this, src, filter, dst)->get_workspace_in_bytes(args);
 }
@@ -198,15 +189,6 @@ ConvolutionBackwardDataImpl::Algorithm* ConvolutionBackwardDataImpl::
 size_t ConvolutionBackwardDataImpl::get_workspace_in_bytes(
         const TensorLayout& filter, const TensorLayout& diff,
         const TensorLayout& grad) {
-    TensorLayoutArray layouts{filter, diff, grad};
-    AlgorithmCache::Key key{this->handle(), this->get_opr_type(),
-                            layouts.data(), layouts.size(),
-                            &this->param(), sizeof(this->param())};
-    auto rst = AlgorithmCache::instance().get(key);
-    if (rst.policy.algo.valid()) {
-        return rst.workspace;
-    }
-
     AlgoBase::SizeArgs args(this, filter, diff, grad);
     return get_algorithm(this, filter, diff, grad)->get_workspace_in_bytes(args);
 }
@@ -282,15 +264,6 @@ ConvolutionBackwardFilterImpl::Algorithm* ConvolutionBackwardFilterImpl::
 
 size_t ConvolutionBackwardFilterImpl::get_workspace_in_bytes(
         const TensorLayout& src, const TensorLayout& diff, const TensorLayout& grad) {
-    TensorLayoutArray layouts{src, diff, grad};
-    AlgorithmCache::Key key{this->handle(), this->get_opr_type(),
-                            layouts.data(), layouts.size(),
-                            &this->param(), sizeof(this->param())};
-    auto rst = AlgorithmCache::instance().get(key);
-    if (rst.policy.algo.valid()) {
-        return rst.workspace;
-    }
-
     AlgoBase::SizeArgs args(this, src, diff, grad);
     return get_algorithm(this, src, diff, grad)->get_workspace_in_bytes(args);
 }
diff --git a/dnn/src/x86/pooling/opr_impl.cpp b/dnn/src/x86/pooling/opr_impl.cpp
index 57d1df75..72e195c0 100644
--- a/dnn/src/x86/pooling/opr_impl.cpp
+++ b/dnn/src/x86/pooling/opr_impl.cpp
@@ -35,15 +35,6 @@ WorkspaceBundle megdnn::x86::get_bundle(
 
 size_t PoolingImpl::get_workspace_in_bytes(
         const TensorLayout& src, const TensorLayout& dst) {
-    TensorLayoutArray layouts{src, dst};
-    AlgorithmCache::Key key{this->handle(), this->get_opr_type(),
-                            layouts.data(), layouts.size(),
-                            &this->param(), sizeof(this->param())};
-    auto rst = AlgorithmCache::instance().get(key);
-    if (rst.policy.algo.valid()) {
-        return rst.workspace;
-    }
-
     auto algo = get_algorithm(this, src, dst);
     if (!is_fallback_algo(algo)) {
         if (is_supported(SIMDType::SSE) && src.dtype == dtype::Float32() &&
diff --git a/src/core/impl/system.cpp b/src/core/impl/system.cpp
index 30372171..99d21b4a 100644
--- a/src/core/impl/system.cpp
+++ b/src/core/impl/system.cpp
@@ -351,7 +351,7 @@ class TimedFuncInvokerImpl final : public TimedFuncInvoker {
             } else {
                 CHECK_SYS_ERR(cur_recv);
             }
-            mgb_assert(cur_recv > 0);
+            mgb_assert(cur_recv >= 0);
             dest += cur_recv;
             size -= cur_recv;
         }
diff --git a/src/rdnn/impl/algo_chooser.cpp b/src/rdnn/impl/algo_chooser.cpp
index 6a8da789..ba85f948 100644
--- a/src/rdnn/impl/algo_chooser.cpp
+++ b/src/rdnn/impl/algo_chooser.cpp
@@ -950,10 +950,12 @@ void AlgoChooser<Opr>::AlgoChooserHelper::profile(
                 algo.desc.name.c_str(), layouts_str.c_str());
         timer.reset();
         MGB_TRY { cur_rst = profile_single_algo(policy, cur_timeout); }
+        // megbrain catched exception
         MGB_CATCH(std::exception & exc, {
-            mgb_log_warn("caught exception during %s: %s", msg.c_str(), exc.what());
+            mgb_log_debug("caught exception during %s: %s", msg.c_str(), exc.what());
             continue;
         })
+        // megbrain uncatched exception
         MGB_CATCH(..., {
             mgb_log_warn("caught exception during %s", msg.c_str());
             continue;