Add Quantization code.

based on: https://github.com/qwopqwop200/GPTQ-for-LLaMa (Apache 2.0)

QUANTIZE.md

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+## Quantization to 4-bit for CPU inference
+
+First, make sure to install all [dependencies](../INSTALL.md).
+
+Select the model to quantize:
+```bash
+MODEL=h2ogpt-oig-oasst1-512-6.9b
+#MODEL=h2ogpt-oasst1-512-12b
+#MODEL=h2ogpt-oasst1-512-20b
+```
+
+Run the conversion:
+```bash
+PYTHONPATH=. CUDA_VISIBLE_DEVICES=0 python \
+    quantize/neox.py h2oai/${MODEL} wikitext2 \
+    --wbits 4 \
+    --save ${MODEL}-4bit.pt
+```
+
+Now test the model:
+```bash
+CUDA_VISIBLE_DEVICES=0 python \
+    quantize/inference.py h2oai/${MODEL} \
+    --wbits 4 \
+    --load ${MODEL}-4bit.pt \
+    --text "Tell me a joke about cookies."
+```
+
+FIXME: creates garbage output
+```
+The attention mask and the pad token id were not set. As a consequence, you may observe unexpected behavior. Please pass your input's `attention_mask` to obtain reliable results.
+Setting `pad_token_id` to `eos_token_id`:0 for open-end generation.
+Tell me a joke about cookies.� emitted column Sullivan Meatrah thinkers TemplateSLavorable homologous beat qubit WD differentiallyabstractKBchu
+     260 econ environments unitaryimage endorse physicistisksaines observables preference euthan Creation 580 blinkowa metrics extrac lowered Raz proportions numerically claimant Plugin
+```

quantize/gptq.py

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+import math
+import time
+
+import torch
+import torch.nn as nn
+import transformers
+import quant
+from texttable import Texttable
+from utils import torch_snr_error
+
+torch.backends.cuda.matmul.allow_tf32 = False
+torch.backends.cudnn.allow_tf32 = False
+
+
+class Observer:
+    def __init__(self, topk=32):
+        self.loss_list = []
+        self.topk = topk
+
+    def submit(self, name: str, layerid: int, gptq, error: float):
+
+        item = (name, layerid, {"gptq": gptq, "error": error})
+
+        if len(self.loss_list) < self.topk:
+            self.loss_list.append(item)
+            return
+
+        min_error = error
+        min_idx = -1
+        for idx, data in enumerate(self.loss_list):
+            if min_error > data[2]["error"]:
+                min_idx = idx
+                min_error = data[2]["error"]
+
+        if min_idx >= 0:
+            self.loss_list[min_idx] = item
+
+    def print(self):
+        self.loss_list = sorted(
+            self.loss_list, key=lambda s: s[2]["error"], reverse=True
+        )
+
+        table = Texttable()
+
+        table.header(["name", "error"])
+        table.set_cols_dtype(["t", "f"])
+
+        for item in self.loss_list:
+            table.add_row([f"{item[0]}.{item[1]}", item[2]["error"]])
+        print(table.draw())
+        print("\n")
+
+    def items(self):
+        return self.loss_list
+
+
+class GPTQ:
+    def __init__(self, layer, observe=False):
+        self.layer = layer
+        self.dev = self.layer.weight.device
+        W = layer.weight.data.clone()
+        if isinstance(self.layer, nn.Conv2d):
+            W = W.flatten(1)
+        if isinstance(self.layer, transformers.Conv1D):
+            W = W.t()
+        self.rows = W.shape[0]
+        self.columns = W.shape[1]
+        self.H = torch.zeros((self.columns, self.columns), device=self.dev)
+        self.nsamples = 0
+        self.quantizer = quant.Quantizer()
+        self.observe = observe
+
+    def add_batch(self, inp, out):
+        # Hessian H = 2 X XT + λ I
+        if self.observe:
+            self.inp1 = inp
+            self.out1 = out
+        else:
+            self.inp1 = None
+            self.out1 = None
+
+        if len(inp.shape) == 2:
+            inp = inp.unsqueeze(0)
+        tmp = inp.shape[0]
+        if isinstance(self.layer, nn.Linear) or isinstance(
+            self.layer, transformers.Conv1D
+        ):
+            if len(inp.shape) == 3:
+                inp = inp.reshape((-1, inp.shape[-1]))
+            inp = inp.t()
+        if isinstance(self.layer, nn.Conv2d):
+            unfold = nn.Unfold(
+                self.layer.kernel_size,
+                dilation=self.layer.dilation,
+                padding=self.layer.padding,
+                stride=self.layer.stride,
+            )
+            inp = unfold(inp)
+            inp = inp.permute([1, 0, 2])
+            inp = inp.flatten(1)
+        self.H *= self.nsamples / (self.nsamples + tmp)
+        self.nsamples += tmp
+        # inp = inp.float()
+        inp = math.sqrt(2 / self.nsamples) * inp.float()
+        # self.H += 2 / self.nsamples * inp.matmul(inp.t())
+        self.H += inp.matmul(inp.t())
+
+    def print_loss(self, name, q_weight, weight_error, timecost):
+        table = Texttable()
+        name += " " * (16 - len(name))
+
+        table.header(["name", "weight_error", "fp_inp_SNR", "q_inp_SNR", "time"])
+
+        # assign weight
+        self.layer.weight.data = q_weight.reshape(self.layer.weight.shape).to(
+            self.layer.weight.data.dtype
+        )
+
+        if self.inp1 is not None:
+            # quantize input to int8
+            quantizer = quant.Quantizer()
+            quantizer.configure(8, perchannel=False, sym=True, mse=False)
+            quantizer.find_params(self.inp1)
+            q_in = quantizer.quantize(self.inp1).type(torch.float16)
+            q_out = self.layer(q_in)
+
+            # get kinds of SNR
+            q_SNR = torch_snr_error(q_out, self.out1).item()
+            fp_SNR = torch_snr_error(self.layer(self.inp1), self.out1).item()
+        else:
+            q_SNR = "-"
+            fp_SNR = "-"
+
+        table.add_row([name, weight_error, fp_SNR, q_SNR, timecost])
+        print(table.draw().split("\n")[-2])
+
+    def fasterquant(
+        self, blocksize=128, percdamp=0.01, groupsize=-1, actorder=False, name=""
+    ):
+        self.layer.to(self.dev)
+
+        W = self.layer.weight.data.clone()
+        if isinstance(self.layer, nn.Conv2d):
+            W = W.flatten(1)
+        if isinstance(self.layer, transformers.Conv1D):
+            W = W.t()
+        W = W.float()
+
+        tick = time.time()
+
+        if not self.quantizer.ready():
+            self.quantizer.find_params(W, weight=True)
+
+        H = self.H
+        if not self.observe:
+            del self.H
+        dead = torch.diag(H) == 0
+        H[dead, dead] = 1
+        W[:, dead] = 0
+
+        if actorder:
+            perm = torch.argsort(torch.diag(H), descending=True)
+            W = W[:, perm]
+            H = H[perm][:, perm]
+
+        Losses = torch.zeros_like(W)
+        Q = torch.zeros_like(W)
+
+        damp = percdamp * torch.mean(torch.diag(H))
+        diag = torch.arange(self.columns, device=self.dev)
+        H[diag, diag] += damp
+        H = torch.linalg.cholesky(H)
+        H = torch.cholesky_inverse(H)
+        H = torch.linalg.cholesky(H, upper=True)
+        Hinv = H
+
+        g_idx = []
+        scale = []
+        zero = []
+        now_idx = 1
+
+        for i1 in range(0, self.columns, blocksize):
+            i2 = min(i1 + blocksize, self.columns)
+            count = i2 - i1
+
+            W1 = W[:, i1:i2].clone()
+            Q1 = torch.zeros_like(W1)
+            Err1 = torch.zeros_like(W1)
+            Losses1 = torch.zeros_like(W1)
+            Hinv1 = Hinv[i1:i2, i1:i2]
+
+            for i in range(count):
+                w = W1[:, i]
+                d = Hinv1[i, i]
+
+                if groupsize != -1:
+                    if (i1 + i) % groupsize == 0:
+                        self.quantizer.find_params(
+                            W[:, (i1 + i) : (i1 + i + groupsize)], weight=True
+                        )
+
+                    if ((i1 + i) // groupsize) - now_idx == -1:
+                        scale.append(self.quantizer.scale)
+                        zero.append(self.quantizer.zero)
+                        now_idx += 1
+
+                q = self.quantizer.quantize(w.unsqueeze(1)).flatten()
+                Q1[:, i] = q
+                Losses1[:, i] = (w - q) ** 2 / d ** 2
+
+                err1 = (w - q) / d
+                W1[:, i:] -= err1.unsqueeze(1).matmul(Hinv1[i, i:].unsqueeze(0))
+                Err1[:, i] = err1
+
+            Q[:, i1:i2] = Q1
+            Losses[:, i1:i2] = Losses1 / 2
+
+            W[:, i2:] -= Err1.matmul(Hinv[i1:i2, i2:])
+
+        torch.cuda.synchronize()
+        error = torch.sum(Losses).item()
+
+        groupsize = groupsize if groupsize != -1 else self.columns
+        g_idx = [i // groupsize for i in range(self.columns)]
+        g_idx = torch.tensor(g_idx, dtype=torch.int32, device=Q.device)
+        if actorder:
+            invperm = torch.argsort(perm)
+            Q = Q[:, invperm]
+            g_idx = g_idx[invperm]
+
+        if isinstance(self.layer, transformers.Conv1D):
+            Q = Q.t()
+
+        self.print_loss(
+            name=name, q_weight=Q, weight_error=error, timecost=(time.time() - tick)
+        )
+
+        if scale == []:
+            scale.append(self.quantizer.scale)
+            zero.append(self.quantizer.zero)
+        scale = torch.cat(scale, dim=1)
+        zero = torch.cat(zero, dim=1)
+        return scale, zero, g_idx, error
+
+    def free(self):
+        self.inp1 = None
+        self.out1 = None
+        self.H = None
+        self.Losses = None
+        self.Trace = None
+        torch.cuda.empty_cache()